What are some alternatives?
When comparing Altospam and Rspamd, 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.
SpamAssassin - Use this program to "Unspam" your mailbox(es).
CryptoPrevent - CryptoPrevent is an Anti-Virus/Security Software Supplement, originally designed in late 2013.
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
AppCheck Anti-Ransomware - Protect your PC with 100% Signatureless Anti-Ransomware AppCheck
Proxmox Mail Gateway - Protect mail server against spam, viruses and malware with Proxmox Mail Gateway security for businesses, government, education and non-profit organizations.