Dovecot is described as 'open source IMAP and POP3 email server for Linux/UNIX-like systems, written with security primarily in mind. Dovecot n excellent choice for both small and large installations' and is an app in the Office & Productivity category. There are eight alternatives to Dovecot for Mac, Linux, BSD, Self-Hosted solutions and Windows. The best alternative is hMail Server, which is both free and Open Source. Other great apps like Dovecot are Cyrus IMAP (Free, Open Source), Mercury Mail Transport System (Free Personal), Magma (Free, Open Source) and Archiveopteryx (Free, Open Source).
The Cyrus IMAP server differs from other IMAP server implementations in that it is generally intended to be run on sealed servers, where normal users cannot log in. Users can access mail through the IMAP/IMAP-S, JMAP, POP3/POP3-S or KPOP protocols.
The Mercury Mail Transport System is a mail server that sends and receives messages on behalf of a group of users on a machine or local area network. Messages from the outside world are received by Mercury and delivered to the users, who can access it at any later point.
Magma is a fully-featured, commercial-grade email server with support for SMTP, POP3, IMAP, HTTP, and an internal protocol MOLTEN. Support for the DIME ecosystem of advanced encryption protocols is currently in active development. Originally created by Ladar Levison for lavabit.
Archiveopteryx is an Internet mail server, optimised to support long-term archival storage. It seeks to make it practical not only to manage large archives, but to use the information therein on a daily basis instead of relegating it to offline storage.