What are some alternatives?
When comparing Altospam and SpamAssassin, you can also consider the following products
Scrollout F1 - Scrollout is a free and easy to use anti-spam email gateway designed for Linux & Windows administrators without advanced email security experience.
CryptoPrevent - CryptoPrevent is an Anti-Virus/Security Software Supplement, originally designed in late 2013.
Proxmox Mail Gateway - Protect mail server against spam, viruses and malware with Proxmox Mail Gateway security for businesses, government, education and non-profit organizations.
AppCheck Anti-Ransomware - Protect your PC with 100% Signatureless Anti-Ransomware AppCheck
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
Mailwasher - Over 8 million people use MailWasher as their spam filter