How to block certain attachment types in Postfix

This document (7000885) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 11
SUSE Linux Enterprise Server 10

Situation

How to block certain attachments based on the extension of the file name

Resolution

1. Launch a Terminal and become the root user. Backup main.cf file located in /etc/postfix directory and edit it.

su -

cp /etc/postfix/main.cf /etc/postfix/main.cf.original

vi /etc/postfix/main.cf

2. Search for the line

# header_checks = regexp:/etc/postfix/header_checks

3. Remove the # (hash) from the above mentioned line and save the file.

4. Backup header_checks file located in /etc/postfix and edit it

cp /etc/postfix/header_checks /etc/postfix/header_checks.original

vi /etc/postfix/header_checks

5. Add the following line at the bottom of the file and save it

/name=[^>]*\.(exe|pif|com|dll|vbs|bat)/ REJECT

(Add other extensions that need to be blocked)

6. Restart the postfix service

/etc/init.d/postfix restart

Additional Information

To test the configuration, send a test message with an attachment type mentioned in the header_checks file

mail -a /path_to_file user_name

put the subject name

end the message with a . (dot)

check the the log file

tail -f /var/log/mail

It will show an entry somthing like this

"Date Time hostname postfix/cleanup[xxxxx]: xxxxxxxxxx: reject: header Content-Disposition: attachment;? filename="filename.extension" from local; from=< user@domain_name > to to=< user@domain_name >: Message content rejected"

Disclaimer

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