ClamAV is an anti-virus software. Set up clamav-milter to check the virus whenever a mail goes through the Postfix.
# apt install clamav-milter
Just installing clamav-milter will install other ClamAV suites required.
Only 1 line in /etc/clamav/clamav-milter.conf, MilterSocket has to be changed to enable Postfix access.
Restart the server. Clamd should be started automatically but it doesn't. Just restarting whole server is the easiest and safest way for the fresh start...
Add clamav-milter to the milter configuration line in /etc/postfix/main.cf.
smtpd_milters = unix:/milter-greylist/milter-greylist.sock unix:/clamav/clamav-milter.ctl
Reload Postfix to apply new milter.
# systemctl reload postfix
Send a clean mail to the account, and check the mail header to find the lines added by ClamAV.
X-Virus-Scanned: clamav-milter 0.101.4 at mail (Here will be the mail server hostname) X-Virus-Status: Clean
If you want to test the infected mail case, you can use the EICAR test virus for this purpose.
Now everywhere is protected by the anti-virus, so it'll be hard to send out infected mail for testing...