The branch 3.X of GNU mailutils fixed the following deficiences found in versions 2.X:
- Provide a consistent and effective interface for stream I/O.
- Reorganize the codebase to use streams API, thereby improving performance.
- Rewrite the filter API to improve its performance and to allow for easy creation and chaining of filters.
- Improve logging and debugging support.
- Provide API for word splitting and variable substitution instead of the obsolete argcv module.
- Rewrite the client support for IMAP4.
- Provide an extensive testsuite for Mailutils API as well as for the particular applications (in 2.X, the testcases were based on DejaGNU and were mostly non-portable).
- Version 3.10, released on August 14, 2020
- Version 3.9, released on March 13, 2020
- Version 3.8, released on November 6, 2019
- Version 3.7, released on June 21, 2019
- Version 3.6, released on February 23, 2019
- Version 3.5, released on October 27, 2018
- Version 3.4, released on December 2, 2017
- Version 3.3, released on October 18, 2017
- Version 3.2, released on March 11, 2017
- Version 3.1.1, released on December 15, 2016
- Version 3.1, released on December 13, 2016
- Version 3.0, released on November 6, 2016, the first stable release
- Version 2.99.94, released on November 6, 2011, the first alpha release of this branch.