What are some alternatives?
When comparing amavisd-new and Proxmox Mail Gateway, you can also consider the following products
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
Scrollout F1 - Scrollout is a free and easy to use anti-spam email gateway designed for Linux & Windows administrators without advanced email security experience.
SpamAssassin - Use this program to "Unspam" your mailbox(es).
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...
Kolab Community - Kolab Groupware is a secure, scalable, reliable, flexible, full-featured collaboration suite.
Akamai - Akamai is the leading content delivery network (CDN) services provider for media and software delivery, and cloud security solutions.