JP7283351B2 - E-mail monitoring device and e-mail monitoring method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a mail checking technique for temporarily retaining sent mail sent from a user in a mail monitoring device and checking the sent mail.

Conventionally, as a mail monitoring technology for preventing erroneous transmission of outgoing mail sent from a sender user, a mail monitoring device connected between a user terminal and a communication network temporarily holds outgoing mail. In addition, Japanese Laid-Open Patent Publication No. 2002-100001 proposes a so-called self-checking method in which the sender user himself/herself checks the sent mail.

Specifically, the method of Patent Document 1 is based on the confirmation items described in the target email to be checked and the confirmation items described in emails sent in the past to the destination specified in the target email. When there is a contradiction between these items to be confirmed, the sender user of the target mail is prompted to check these items to be confirmed.
As a result, since the mail monitoring device keeps the target mail for a certain period of time, when the sending user notices an error due to the reminder from the mail monitoring device, the mail transmission to the mail monitoring device is canceled. can be done. Also, if the sending user does not cancel within a certain period of time, the target mail will be automatically sent.

Japanese Patent No. 5876181

The prior art described in Patent Literature 1 described above is a so-called self-checking method in which the sender user who sent the target mail rechecks the target mail. However, in order to prompt the sender user to recheck, it is necessary to accumulate past sent mails in the mail monitoring device and compare the check items of these past sent mails with the target mail. As a result, there is a problem that the hardware scale and processing load of the mail monitoring device increase significantly.

SUMMARY OF THE INVENTION It is an object of the present invention to solve such problems, and to provide a mail checking technique that enables a sender user to recheck sent mail with a relatively simple configuration.

In order to achieve such an object, the mail monitoring apparatus according to the present invention comprises a storage circuit for temporarily storing an outgoing mail with an attached file sent from a user terminal; a control circuit for relaying and transferring the original transmission mail obtained from the storage circuit to the mail server in response to a transmission destination notification mail for notifying the transmission destination of the password used for encrypting the attached file, The circuit generates a password to be used for encryption processing of the attached file, and notifies the user terminal of the password by a notification mail for sender, and in response to notification of the password by the notification mail for sender, a destination confirmation unit for confirming a destination email address of the destination notification email sent from the user terminal; an encryption processing unit for encrypting an attached file of the email to be sent based on the password; The destination e-mail address confirmed by the destination confirmation unit is used as a destination, and the transmission mail having the attached file encrypted by the encryption processing unit is relayed and transferred to the mail server. and a relay processing unit that relays and transfers the notification mail to the mail server.

Further, a mail monitoring method according to the present invention includes a storage circuit for temporarily storing an outgoing mail with an attached file sent from a user terminal, and a password used for encrypting the attached file sent from the user terminal. and a control circuit for relaying and transferring the original transmission mail obtained from the storage circuit to a mail server according to the destination notification mail for notifying the destination of the mail monitoring method. a password notification step in which the control circuit generates a password used for encryption processing of the attached file and notifies it to the user terminal by means of a transmission source notification mail; a destination confirmation step of confirming a destination e-mail address of the destination notification e-mail transmitted from the user terminal in response to the notification of the password by the user terminal; an encryption processing step of encrypting the attached file, and the control circuit uses the destination mail address confirmed in the destination confirmation step as a destination, and encrypts the attached file in the encryption processing step. and a relay processing step of relaying the transmitted mail to the mail server and relaying the destination notification mail to the mail server.

According to the present invention, the source user of the user terminal can recheck the destination address included in the original transmission mail in the notification mail for the source, and the wrong destination among the destination addresses can be sent. It is possible to send destination notification mail only to correct destinations without sending destination notification mail. Therefore, in the mail monitoring device, the original transmission mail is transmitted only to the destination to which the transmission destination notification mail was transmitted from the transmission source user, that is, to the correct transmission destination.

Therefore, there is no need to accumulate past sent mails and compare the items to be confirmed in these past sent mails with the target mail. Therefore, as a result, the function of exchanging the notification mail for the sender and the notification mail for the destination with the user terminal, and the function of analyzing these mails, without greatly increasing the hardware scale and processing load of the mail monitoring device. With such a relatively simple configuration, the sender user can recheck the sent mail.

1 is a block diagram showing the configuration of an email monitoring system; FIG. FIG. 4 is an explanatory diagram showing a configuration example of an outgoing mail; FIG. 4 is an explanatory diagram showing a configuration example of a password list; FIG. 10 is an explanatory diagram showing a configuration example of a sender notification mail; FIG. 4 is an explanatory diagram showing a configuration example of a destination notification mail; FIG. 4 is an explanatory diagram showing a configuration example of an outgoing mail that is permitted to be sent; FIG. 10 is a sequence diagram showing a sent mail check operation;

Next, one embodiment of the present invention will be described with reference to the drawings.
[Mail monitoring system]
First, a mail monitoring device 10 according to the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of a mail monitoring system.
As shown in FIG. 1, this mail monitoring device 10 is connected between n (n is an integer equal to or greater than 1) user terminals (#1, #2, . . . , #n) 20 and a communication network NW. It is a device that monitors e-mails sent and received between the mail server 30 of the communication network NW and the user terminal 20 .

The user terminal 20 is generally composed of an information terminal such as a PC, a tablet, and a smartphone, and is connected to the mail monitoring device 10 via a wired or wireless communication line L2. It has a function to send and receive e-mail.
The communication network NW consists of a data communication network such as the Internet, and includes a mail server 30 that accumulates and distributes e-mails, and partner terminals (#1, #2) with which e-mails are exchanged with the user terminal 20. ) 31 are connected.

[Principle of Invention]
The principle of the present invention will be explained. The method of temporarily storing the sent mail from the user terminal 20 in the mail monitoring device 10 and rechecking the destination and the body of the sent mail during that time is extremely effective from the viewpoint of preventing erroneous sending of the mail. target. However, in the case of the above-described conventional self-checking method, it is necessary to accumulate past sent mails in the mail monitoring device 10 and compare the check items of these past sent mails with the target mails. Therefore, the hardware scale and processing load of the mail monitoring device 10 are greatly increased.

Further, it is difficult to extract errors and prevent erroneous transmissions with high accuracy, even if all sent mails are simply urged to be rechecked by the sender. This is because the source user who created the outgoing mail rechecks the destination and the mail body of the target mail, and there is a high possibility that checks will be omitted due to assumptions.

In general, when an e-mail contains important confidential information, erroneous transmission of the e-mail becomes a big problem. As one of the methods to deal with such erroneous transmission, when sending important confidential information by e-mail, after describing the confidential information in an attached file, encrypt it with a password and attach it to the e-mail. There is a method of notifying the destination by a password notification mail (hereinafter referred to as destination notification mail) separate from the transmission mail. As a result, even if an erroneous transmission is found after sending the outgoing mail, the attached file cannot be decrypted unless the destination notification mail is sent, thereby preventing leakage of confidential information.

In order to reduce the workload of the sender user in such a method, the email monitoring device 10 automatically generates a password and sends a password notification email (hereinafter referred to as a notification for the sender) when an outgoing email containing an attached file is received. mail) to notify the source user and prompt the destination user to create a destination notification mail.
At this time, when the sender notification mail is received from the mail monitoring device 10, the sender user creates a destination notification mail for the destination based on the password notified in the sender notification mail. is transmitted to the mail server 30 via the mail monitoring device 10. FIG.

Here, when the source user creates the destination notification mail for the destination, the source user reconfirms the destination mail address of the original transmission mail. The present invention focuses on the reconfirmation of the destination mail address by the source user in the work of creating the destination notification mail for the destination. The reconfirmation of the address is used for rechecking the sent mail.

Specifically, when reconfirming the destination email address, if the sender notices that an incorrect destination is included in the original email, a notification email for the incorrect destination is sent. It is possible to send destination notification mails only to correct destinations. Using this fact, the mail monitoring device 10 monitors the destination notification mail from the source user, extracts the destination as the correct destination, and transmits the original transmission mail only to the correct destination. It is designed to A specific configuration for realizing the mail check method according to the present invention will be described below.

[Configuration of mail monitoring device]
As shown in FIG. 1, the mail monitoring device 10 has, as main circuit configurations, a network interface circuit (hereinafter referred to as network I/F circuit) 11, a terminal interface circuit (hereinafter referred to as terminal I/F circuit) 12, a memory A circuit 13 and a control circuit 14 are provided.

[Interface circuit]
The network I/F circuit 11 is a circuit for transmitting/receiving various data such as protocol messages related to e-mail and mail data to/from the communication network NW via a wired or wireless communication line L1.
The terminal I/F circuit 12 is a circuit for transmitting/receiving various data such as protocol messages related to e-mail and mail data to/from the user terminal 20 via a wired or wireless communication line L2.

[Memory circuit]
The storage circuit 13 is a storage device such as a hard disk or a semiconductor memory, and is a circuit for storing various processing data and programs 13P used for mail monitoring processing in the mail monitoring device 10 .
The program 13P is a program that realizes various processing units for executing mail monitoring processing by cooperating with the CPU of the control circuit 14. The program 13P is a program that implements various processing units for executing mail monitoring processing. (not shown) and stored in the storage circuit 13 in advance.

As main processing data stored in the memory circuit 13, there are a retained mail 13A and a password list 13B.
The retained mail 13A is an original sent mail (original sent mail) sent from the user terminal 20 and stored in the storage circuit 13 by the control circuit 14 . FIG. 2 is an explanatory diagram showing a configuration example of an outgoing mail. As shown in FIG. 2, an outgoing mail is composed of various items such as a destination address, a sender address, a subject, and a body of the mail, and data indicating the contents thereof. In this example, two addresses "aaa@aaa.jp" and "bbb@bbb.jp" are specified as the destination addresses, and "xxx@xxx.jp" is specified as the source address.

In addition, contents that are not suitable for writing in the body of the mail, such as important confidential information, are stored in a separate electronic file by the sender user and attached as an attachment to the outgoing mail. In the example of FIG. 2, an attached file with the file name "project X.doc" is attached to the outgoing mail. Specific examples of attached files include document files and drawing files created with a PC, and photo files taken with a camera. This attached file is encrypted with a password automatically generated by the control circuit 14 and then sent to the mail server 30 .

The password list 13B is a list in which pairs of passwords used for encryption processing of attached files and source addresses of original transmission mails are registered. This password list 13B is for checking whether the same password is used for pending mail, and is automatically generated by the control circuit 14 of the mail monitoring device 10 when an outgoing mail is received. Registered in list 13B. FIG. 3 is an explanatory diagram showing a configuration example of a password list. As shown in FIG. 3, passwords and source addresses are registered as pairs in the password list 13B.

Specifically, "hagr21vas" and "j45rsfas2" are generated and registered for "XXX@XXX.jp" and "YYY@YYY.jp", respectively. When a password is generated, if there is the same password as the generated password in the password list 13B, a different password is generated.

Also, in FIG. 3, a case where a password and a source address are registered as a set has been described as an example, but the present invention is not limited to this. For example, mail identification information for identifying the sent mail itself may be added to the set of the password and the destination address. As a result, even when a plurality of outgoing mails with attached files are sent from the same source mail address at the same time, a different password can be used for each outgoing mail, improving the security of the attached files. can be done.

[Control circuit]
The control circuit 14 includes a CPU and its peripheral circuits, and by reading and executing a program 13P from the storage circuit 13, realizes various processing units for executing mail monitoring processing.
Main processing units realized by the control circuit 14 include a relay processing unit 14A, a password notification unit 14B, a destination confirmation unit 14C, and an encryption processing unit 14D. These processing units are configured to perform the functions described below, but the relationship between these processing units and functions is not limited to the following, and specific functions can be performed by other processing units. may be realized.

[Relay processing unit]
The relay processing unit 14A has a function of exchanging outgoing mail and incoming mail with the mail server 30 via the communication network NW, the communication line L1, and the network I/F circuit 11; A function of exchanging outgoing mail and incoming mail with the user terminal 20 via the F circuit 12, a function of relaying outgoing mail from the user terminal 20 to the mail server 30, and a function of transferring incoming mail from the mail server 30. and a function of relaying to the user terminal 20 .

Further, the relay processing unit 14A has a function of temporarily storing the transmitted mail in the storage circuit 13 as the retained mail 13A when an attached file is attached to the transmitted mail from the user terminal 20, and a function of temporarily storing the transmitted mail as the accumulated mail 13A, and and a function of relaying the sender notification mail received from the mail server 30 to the specified destination user terminal 20, i.e., the sender user terminal of the original transmission mail. It has a function to distribute.

In addition, the relay processing unit 14A has a function of acquiring an original transmission mail from the accumulated mail 13A in the storage circuit 13 according to the destination notification mail transmitted from the user terminal 20, and a function of acquiring the original transmission mail from the destination notification mail. The destination mail address confirmed by the destination confirmation unit 14C is set as the destination, and the transmission mail with the attached file encrypted by the encryption processing unit 14D is relay-transferred to the mail server 30, and the notification for the destination It also has a function of relaying mail to the mail server 30 .

[Password notification part]
The password notifying unit 14B has a function of generating a different password for each outgoing mail as a password used for encrypting the attached file when the relay processing unit 14A receives an outgoing mail with an attached file from the user terminal 20. , a function of registering a pair of a generated password and a sender's e-mail address in the password list 13B of the storage circuit 13; It also has a function of sending mail to the user terminal that sent the mail.

FIG. 4 is an explanatory diagram showing a configuration example of the notification mail for sender. As shown in FIG. 4, the sender's notification mail consists of various items such as a destination address, a sender's address, a title, and a body of the mail, and data indicating the contents thereof. In this example, "XXX@XXX.jp", which is the sender's email address of the original outgoing email, is specified as the destination address, and "XXX@XXX.jp", which is the same as the sender's address, is specified as the sender's address. It is

In addition, the subject is described as "Password notification email (for sender)", and the email is a notification email for sender to notify the password to the sender of the original email (original email). It is specified that
In addition, the text of the email should include an explanation of the notification email for the sender, an explanation of the check work that the sender user should perform based on this notification email for the sender, the preparation of the notification email for the recipient, and An explanation is provided to the effect that the original outgoing mail will be sent accordingly.

Also, in the body of the email, the password created for each original sent email is described. As a result, the sender user can easily recheck the destination e-mail address specified in the original e-mail in addition to the password. can be easily created.

FIG. 5 is an explanatory diagram showing a configuration example of a destination notification mail. As shown in FIG. 5, the destination notification mail consists of various items such as a destination address, a source address, a subject, and a body of the mail, and data indicating the contents thereof. In this example, "aaa@aaa.jp", which is one of the destination addresses of the original outgoing mail, is specified as the destination address, and "xxx @xxx.jp" is described.

In addition, the subject says "Password notification mail (for destination)", and the mail is a notification mail for the destination to notify the password to the destination of the original transmission mail (original mail). One thing is stated.
The text of the mail also includes an explanation of the destination notification mail, a password and attached file to be notified in this destination notification mail, and an explanation of the original transmission mail.

When the source user finds an error in the rechecked destination e-mail address in the source notification mail, the source user can create and transmit the destination notification mail only to the correct destination. As a result, the original transmission mail is transmitted from the mail monitoring device 10 to the mail server 30 only to the correct destination specified in the destination notification mail from the source user terminal.

[Destination confirmation part]
When the relay processing unit 14A receives the destination notification mail from the source user terminal in response to the notification of the password by the source notification mail, the destination confirmation unit 14C checks the destination mail for the destination notification mail. It has a function of confirming the address and a function of acquiring the password corresponding to the sender's mail address from the password list 13B of the storage circuit 13. FIG.

[Encryption processing part]
The encryption processing unit 14D has a function of encrypting the attached file included in the original transmission mail acquired from the storage circuit 13 by the relay processing unit 14A based on the password acquired by the destination confirmation unit 14C. .

FIG. 6 is an explanatory diagram showing a configuration example of an outgoing mail that is permitted to be sent. As shown in FIG. 6, in response to the destination notification mail from the source user terminal, the mail sent to the mail server actually sent from the mail monitoring device 10 to the mail server 30 consists of a destination address, a source It consists of various items such as the address, subject, mail body, etc., and data indicating the contents of the items.

For example, when only the destination notification mail to the transmission address "aaa@aaa.jp" is transmitted from the source user terminal, the destination address of the original transmission mail is "aaa@aaa.jp" as shown in FIG. jp" is changed. Also, the attached file is replaced with an encrypted file (compressed file) encrypted by the encryption processing unit 14D, and the file name is changed to "project X.lzh".

Here, regarding "bbb@bbb.jp" specified as the destination address in the original sent mail, the sender notices that the sender has sent an erroneous transmission, and the destination notification mail was not sent from the sender's terminal. , the mail monitoring device 10 does not send an outgoing mail regarding "bbb@bbb.jp" to the mail server.

[Operation of this embodiment]
Next, an email monitoring method of the email monitoring device 10 according to the present embodiment will be described with reference to FIG. FIG. 7 is a sequence diagram showing a sent mail check operation.
Here, based on the transmitted mail shown in FIG. 2, an example will be described in which the user terminal #1 rechecks the transmitted mail from the user terminal #1.

In user terminal #1, when the source user creates a transmission mail with an attached file (step 100) and performs a transmission operation (step 101), user terminal #1 requests transmission of the transmission mail regarding the transmission mail. (step 102).

The relay processing unit 14A of the mail monitoring device 10 receives the transmitted mail with the attached file in response to the mail transmission request from the user terminal #1, and stores it in the storage circuit 13 as the retained mail 13A (step 103).

The password notification unit 14B generates a password to be used for encrypting the attached file for each original transmission mail received by the relay processing unit 14A, and stores the combination of the password and the sender's mail address in the password list 13B of the storage circuit 13. (step 104).

When the outgoing mail shown in FIG. 2 is received, since "XXX@XXX.jp" is specified as the sender's address, a different password is generated for each sender's email address. In the example of FIG. 3, "hagr21vas" and "j45rsfas2" are generated and registered for "XXX@XXX.jp" and "YYY@YYY.jp", respectively.

Further, the password notification unit 14B creates a transmission source notification mail as shown in FIG. The relay processing unit 14A transmits this source notification mail to the mail server 30 via the network I/F circuit 11, communication line L1 and communication network NW (step 106).

Subsequently, the relay processing unit 14A receives the sender notification mail from the mail server 30 via the communication network NW, the communication line L1, and the network I/F circuit 11 (step 110). and delivered to user terminal #1 via communication line L2 (step 111).

The source user of user terminal #1 checks the source notification mail received from the mail monitoring device 10 (step S112), and confirms the password generated by the mail monitoring device 10 based on the text. Also, check the destination address specified in the original outgoing mail.

Thereafter, the source user creates a destination notification mail only for correct destinations among the checked destination addresses (step 113), and performs a transmission operation (step 114). As a result, the user terminal #1 requests the mail monitoring device 10 to send the destination notification mail (step 115).
Therefore, in the example of FIG. 4, if the destination address "aaa@aaa.jp" is correct and the destination address "bbb@bbb.jp" is incorrect, the user terminal #1 sends the destination address "aaa@aaa.jp". jp" will be sent.

When the relay processing unit 14A of the mail monitoring device 10 receives the destination notification mail from the user terminal #1, it acquires the original transmission mail corresponding to the destination notification mail from the accumulated mail 13A in the storage circuit 13 ( step 120).

Further, the destination confirmation unit 14C confirms the destination e-mail address of the destination notification mail (step 121), and acquires the password corresponding to the source e-mail address from the password list 13B of the storage circuit 13. (Step 122).

Subsequently, the encryption processing unit 14D encrypts the attached file attached to the original transmission mail acquired by the relay processing unit 14A based on the password acquired by the destination confirmation unit 14C (step 123). .

After that, the relay processing unit 14A corrects the destination address of the original transmission mail to the destination mail address confirmed by the destination confirmation unit 14C, and the encrypted file obtained by the encryption processing unit 14D. After correcting it as an attached file (step 124), it is relay-transferred to the mail server 30 (step 125).
Further, the relay processing unit 14A relays the destination notification mail received from the user terminal #1 to the mail server 30 (step 126).

As a result, for example, when only the destination notification mail to the transmission address "aaa@aaa.jp" is transmitted from the user terminal #1, as shown in FIG. @aaa.jp", the attached file is replaced with an encrypted file (compressed file) encrypted by the encryption processing unit 14D, and the file name is "project X.lzh". , and relay-transferred to the mail server 30.

As a result, the sender notices that "bbb@bbb.jp" specified as the destination address in the original sent mail was sent by mistake and does not send the destination notification mail from user terminal #1. Therefore, the mail monitoring device 10 does not create or send an outgoing mail regarding "bbb@bbb.jp" addressed to the mail server. Also, the original transmission mail itself to "bbb@bbb.jp" is not transmitted from the mail monitoring device 10 to the mail server 30. FIG. After sending the mail, the password associated with the sent mail is deleted from the password list 13B (step 129).

The partner terminal 31 receives the transmission mail from the user terminal #1 from the mail server 30 (step 127), and also receives the destination notification mail from the user terminal #1 (step 128).
Thereby, the partner user of the partner terminal 31 can decrypt (decompress) the attached file attached to the transmission mail based on the password described in the destination notification mail, and can open the original attached file.

[Effects of this embodiment]
As described above, in the present embodiment, in the mail monitoring device 10, the password notification unit 14B generates a password to be used for encryption processing of an attached file, notifies the user terminal 20 by a sender notification mail, and transmits the password. The destination confirmation unit 14C confirms the destination email address of the destination notification email from the user terminal 20, and the relay processing unit 14A sets the destination email address confirmed by the destination confirmation unit 14C as the destination, The encryption processing unit 14D relays the transmission mail with the attached file encrypted with the password to the mail server 30, and relays the destination notification mail from the user terminal 20 to the mail server 30. .

As a result, the sender user of the user terminal 20 can recheck the destination address included in the original sent mail in the notification mail for the sender, and the wrong destination among the destination addresses can be corrected for the destination. It is possible to send notification emails only to correct recipients without sending notification emails. Therefore, in the mail monitoring device 10, the original transmission mail and the transmission destination notification mail are transmitted only to the transmission destination of the transmission destination notification mail transmitted from the transmission source user, that is, to the correct transmission destination.

Therefore, there is no need to accumulate past sent mails and compare the items to be confirmed in these past sent mails with the target mail. For this reason, as a result, the function of exchanging the notification mail for the sender and the notification mail for the recipient with the user terminal 20 and the analysis of these mails can be achieved without greatly increasing the hardware scale and processing load of the mail monitoring device 10. With a relatively simple configuration such as the function to

[Expansion of Embodiment]
Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a non-contradictory range.

DESCRIPTION OF SYMBOLS 10... Mail monitoring apparatus 11... Network interface circuit (network I/F circuit) 12... Terminal interface circuit (terminal I/F circuit) 13... Storage circuit 13A... Remaining mail 13B... Password list 13P... Program , 14... control circuit, 14A... relay processing unit, 14B... password notification unit, 14C... transmission destination confirmation unit, 14D... encryption processing unit, 20, #1, #2, ~, #n... user terminal, 30... mail server, 31, #1, #2... partner terminal, L1, L2... communication line, NW... communication network.

Claims (2)

a storage circuit for temporarily storing a sent mail with an attached file sent from a user terminal;
The original transmission mail obtained from the storage circuit is relayed to a mail server in response to a transmission destination notification mail for notifying a transmission destination of a password used for encrypting the attached file, which is transmitted from the user terminal. and a control circuit for
The control circuit is
a password notification unit that generates a password used for encryption processing of the attached file and notifies the user terminal of the password using a transmission source notification mail;
a destination confirmation unit for confirming a destination email address of the destination notification email transmitted from the user terminal in response to notification of the password by the transmission source notification email;
an encryption processing unit that encrypts an attached file of the outgoing mail based on the password;
setting the destination mail address confirmed by the destination confirmation unit as a destination, and relaying and transferring the transmission mail having the attachment file encrypted by the encryption processing unit to the mail server; A mail monitoring device, comprising: a relay processing unit that relays a notification mail for use to the mail server. A storage circuit for temporarily storing a sent mail with an attached file sent from a user terminal, and a sending destination for notifying a sending destination of a password used for encrypting the attached file sent from the user terminal A mail monitoring method used in a mail monitoring device comprising a control circuit for relaying and forwarding an original transmission mail acquired from the storage circuit to a mail server according to a notification mail,
a password notification step in which the control circuit generates a password to be used for encryption processing of the attached file and notifies the user terminal of the password by a transmission source notification mail;
a destination confirmation step in which the control circuit confirms a destination e-mail address of the destination notification mail transmitted from the user terminal in response to notification of the password by the transmission source notification mail;
an encryption processing step in which the control circuit encrypts an attached file of the outgoing mail based on the password;
The control circuit uses the destination e-mail address confirmed in the destination confirmation step as a destination, and relays and transfers the transmission e-mail in which the attached file is encrypted in the encryption processing step to the mail server. and a relay processing step of relaying and transferring the destination notification mail to the mail server.

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