SpamAssassin - Use this program to "Unspam" your mailbox(es).
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...
Nylas Mail - The Nylas Cloud API powers your application with email, calendar & contacts features. Built-in features for better email, calendar, and contact management.