The classic email sending library for PHP
PHP Email address validator
Anti-Spam SMTP Proxy Server implements multiple spam filters
Universal server
EasyMailer: Bulk Email/SMS Sender Using SMTP
Powerful Open Source Email Marketing app with analytics & segmentation
Simple-to-use/-install issue-tracking system: web, REST, email, CLI
SaltOS, ERP, CRM, Business Management Suite, Josep Sanz Campderrós
Remote anti spam utility
Comprehensive mailing tools for PHP
Web and API based SMTP testing
Python API for Sendmail Milters.
Simple, modern & fast web-based email client
Phishing Campaign Toolkit
Zimbra Domain Admin for Zimbra Open Source Edition
Multi-protocol server written in Java