gpgmailencrypt can encrypt e-mails and check for spam and viruses.
It supports
- PGP/Inline
- PGP/Mime
- S/Mime
For spam checking it supports
- spamassassin
- bogofilter
For virus checking it supports
- avast
- bitdefender
- clamav
- drweb
- f-prot
- sophos
It can be used normally as a script doing everything on command line, in daemon mode, where gpgmailencrypt acts as an encrypting smtp server or as a module for programmers.
It takes e-mails and returns the e-mail encrypted to another e-mail server if a encryption key exists for the receiver. Otherwise it returns the e-mail unencrypted. The encryption method can be selected per user.
See gpgmailencrypt documentation.pdf for more info.(https://github.com/gpgmailencrypt/gpgmailencrypt/blob/master/documentation/gpgmailencrypt%20documentation.pdf)