If you’ve upgraded to 4.1 beta 1, you will probably want to update. This release adds a few bug fixes. In 4.1b1 the progress bar was not lined up right, one of the main toolbar icons did not match the internal icons, and a couple things that didn’t correctly follow the dark theme (when enabled) have been fixed. The help file has been updated to include the new 4.1 options.
The only major non-bugfix change in this release is that IMAP is no longer a dll/plugin, but built into the core. This appears to have speed improvements for IMAP accounts, and more importantly, driving this change, it will make IMAP issues MUCH easier to debug. The installer will automatically remove the previous IMAP plugin for upgrade installations.