Going to look into some email security products, mainly aimed at enteprises. Gateway implementation is main focus. This is in progress and just a list of products atm.
- https://www.mailscanner.info
- https://www.baruwa.com/ (Baruwa is a web-based GUI that provides complete installation and configuration of MailScanner.)
- https://www.mailborder.com/ (Mailborder is a web-based GUI that provides complete installation and configuration of MailScanner)
- http://mailwatch.org/ (A web based front-end to MailScanner
- http://www.scrolloutf1.com/
- https://www.hmailserver.com/
- http://www.radical-spam.org/
- http://spamassassin.apache.org/
- https://sourceforge.net/p/assp/wiki/Main_Page/
- https://openas.org/
- http://www.xeams.com/
- http://www.titanhq.com/
- https://www.roaringpenguin.com/products/canit-pro
- http://www.mailcleaner.org/ (really old?)
- https://nocroom.com/datacenter/spamfirewall/
- http://www.pyzor.org/
- https://www.proxmox.com/en/downloads
- https://www.proxmox.com/
- https://halon.io/
- https://www.sophos.com/en-us/products/secure-email-gateway/tech-specs.aspx