Ecosystem:Mail

Dovecot

Provider -- Timo Sirainen and other contributors
Website -- http://dovecot.org/
License -- open source (MIT and LGPLv2)
Interoperability level -- explicitly supports PostgreSQL with no specific version
Verified PostgreSQL versions -- didn't actually run the program, but just checked the documentation
Last update (YYYY-MM-DD) -- 2016-7-15
Description -- Dovecot is a lightweight, fast, and easy-to-set-up POP3 and IMAP mail server for Unix-like systems. Dovecot can use PostgreSQL for user and password management.
Additional info -- click here

Provider -- Philip Hazel and Exim Development Team
Website -- http://www.exim.org/
License -- open source (MIT and LGPLv3)
Interoperability level -- explicitly supports PostgreSQL with no specific version
Verified PostgreSQL versions -- didn't actually run the program, but just checked the documentation
Last update (YYYY-MM-DD) -- 2016-7-15
Description -- Exim is a mail transfer agent (MTA) for Unix-like systems. It has a great deal of flexibility in routing mails and has extensive facilities for checking incoming mails. Exim is the default MTA on Debian Linux distribution.
Additional info -- click here

Provider -- Software Research Associates, Inc.
Website -- http://www.sra.co.jp/maildepot/
License -- proprietary
Interoperability level -- explicitly supports PostgreSQL with no specific version
Verified PostgreSQL versions -- didn't actually run the program, but just checked the documentation
Last update (YYYY-MM-DD) -- 2016-7-15
Description -- MailDepot is a email archive system tgat can store up to 50 TB of emails, which corresponds to emails of 10,000 users for 5 years. MailDepot copies emails from existing mail servers such as Microsoft Exchange, Lotus Notes/Domino, Sendmail, and Postfix. In addition, it can archive emails from cloud email services such as Google Apps for Business and Microsoft Office 365. MailDepot can perform real-time full text search against one million emails within a second.
Additional info --

Provider -- Wietse Venema and many others
Website -- http://www.postfix.org/
License -- open source (IBM Public License 1.0)
Interoperability level -- explicitly supports PostgreSQL with no specific version
Verified PostgreSQL versions -- didn't actually run the program, but just checked the documentation
Last update (YYYY-MM-DD) -- 2016-7-15
Description -- Postfix is a mail transfer agent (MTA) for Unix-like systems. It can use PostgreSQL for address rewriting and mail routing.
Additional info -- click here