Found a nasty bug in the account edit screen in 5.1.1 that can cause accounts to disappear when editing account information. Beta release users, please upgrade. If you prefer less buggy “stable” releases, please continue to use 5.0.15.
X-Mailer header is now hidden from the preview window unless X-mailer display is enabled in preview options.
IMAP Mark read/unread actions for the the preview window (still experimental).
IMPORTANT! Account editing: switching tabs in 5.1.1 (and possibly 5.1.0?) will cause the wrong tab to display in the UI, so saving accounts will overwrite one or more accounts with a different account.
In older version(s) the progress bar for the preview window did not have the correct z-order and could not be seen depending on which tab was selected.
IMAP Quick Check with “recent messages only” mode enabled was downloading UIDs for all messages in the inbox instead of only the N most recent messages. Eliminating this improved check speed considerably for IMAP.
Some options tabs with quickhelp tooltips were not responding to the quick help cursor and now are selectable. (Known bug: Quick help still does not work when themes are enabled)
Protocol plugins support removed, to make way for IMAP improvements like inbox filtering (eg: unread only) that the plugin architecture was not designed to support.
More refactoring, especially in the account check and preview areas, to facilitate the future possibility of possible future features like background account checking, changing how much of the message downloads on preview, etc.