Self-hosted cloud and mail servers: Nextcloud, Xeams, Open365, MailEnable and hMailServer.
Free, open-source self-hosted file sync and collaboration platform: files, sharing, Calendar, Contacts, Talk, Mail and Office editing with LDAP/AD and SSO. Server runs on Linux or Docker (All-in-One); sync clients for Windows, macOS, Linux, iOS and Android.
Java-based email server and email firewall for Windows, Linux, macOS and UNIX: spam and virus filtering, archiving, encryption and SMTP/POP3/IMAP, in front of Exchange or Microsoft 365. Shareware (conditionally free): Community Edition for personal use only.
Open365 was a free AGPL-3.0 self-hosted suite from eyeOS combining LibreOffice Online, Seafile, KDE Kontact and Jitsi. It never left beta and has been abandoned since December 2016, with no official successor; Nextcloud with an online office suite is the usual replacement.
Windows Server mail server with SMTP, POP3, IMAP, AJAX webmail, list server and web admin. The Standard edition is free for personal and commercial use with unlimited domains; paid editions add ActiveSync, advanced anti-spam and clustering.
Free, open-source (AGPL-3.0) SMTP, POP3 and IMAP mail server for 64-bit Windows. Runs as a service with SQL storage, DKIM, SPF, DMARC and TLS 1.3. Version 5.7.1 fixes a script-injection flaw, so upgrade older 5.6 servers.
