What are some alternatives?
When comparing amavisd-new and SpamAssassin, 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.
Proxmox Mail Gateway - Protect mail server against spam, viruses and malware with Proxmox Mail Gateway security for businesses, government, education and non-profit organizations.
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...
Mailwasher - Over 8 million people use MailWasher as their spam filter
Akamai - Akamai is the leading content delivery network (CDN) services provider for media and software delivery, and cloud security solutions.