1.stalwartlabs / stalwartAll-in-one Mail & Collaboration server. Secure, scalable and fluent in every protocol (IMAP, JMAP, SMTP, CalDAV, CardDAV, WebDAV).imapjmapmailrustserversmtp+4 moreRustNo license16K total1K forks+3,114 starsfrom 12,511 · score 8.04
2.cypht-org / cyphtCypht: Lightweight Open Source webmail aggregator [PHP, JS]. Supports IMAP/SMTP, JMAP and EWS (Exchange Web Services)phpwebmailwebmail-clientimappop3smtp+6 morePHPLGPL-2.11.8K total256 forks+312 starsfrom 1,475 · score 5.75