Rspamd is an open-source email security engine designed to filter phishing, business email compromise, malicious attachments, and spam.
Alternatives to MailRoute
SPAMfighter is Windows software for filtering unwanted email in supported mail programs.
Xeams is an email server and spam firewall that can run on its own, sit in front of another mail server, or work in hybrid mode.
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Apache SpamAssassin
Apache SpamAssassin is free, open-source software that classifies email and helps system administrators block unsolicited bulk messages.
Free planOpen sourceAPILinuxmacOSSelf-hosted7.4Free plan - 5
Avidemux
Free planOpen sourceWebLinuxmacOSWindows7.3Free plan - 6

Mailprotector
Mailprotector builds and supports products for securing and managing organizational email, and says its products are made exclusively for managed service providers (MSPs).
Free planWebAPI7.0Free plan - 7
MailChannels Inbound Filtering
MailChannels Inbound Filtering is a cloud gateway for hosting providers that run email at scale.
WebAPI6.1 - 8
MX Guarddog
MX Guarddog is a cloud email gateway for standard SMTP servers used with owned domains.
Web6.1$0.25 usage-based - 9
SpamSieve
SpamSieve is a macOS application that adds spam filtering to compatible Mac mail programs.
macOS6.1$39.99 one-time - 10

SpamTitan Gateway
SpamTitan Gateway is an anti-spam appliance for administrators who need to control mail flow and protect networks from unwanted email and malware.
WebSelf-hosted5.8 - 11
GFI MailEssentials
GFI MailEssentials is an anti-spam and email security solution for on-premise mail servers.
Self-hostedWindows5.6 - 12
SpamBrella
Web4.7 - 134.6
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MIMEDefang
Linux4.4 - 154.3
- 164.3