Some manual testing around RC5 revealed some bugs, mostly in the Settings -> Servers page around adding and removing IMAP, POP3, and SMTP servers. The following fixes have been included since RC5:
53a4971 - couple libsodium related fixes *
a536cca - use libsodium for encryption if it's available *
5926ab9 - version bump
1b81d10 - don't allow duplicate servers with the same username for SMTP/IMAP/POP3
d6f286d - fix connection test pop3 function I accidentally deleted
ff86ea2 - fixes for smtp server page issues
c17a4e4 - pop3 module set fixes around adding/deleting/forgetting servers
53a9b30 - fix "forget credentials" IMAP form results
2ced896 - fix folder prefetch error message when adding an IMAP server
ad3fa34 - fix a bug restoring local session settings
3e8b00a - fix some layout issues with IMAP message parts and headers
* Libsodium support is not technically a "fix", but it is a well tested security enhancement, and if existing users of the master branch switch to the 1.0.0 release, they could run into compatibility issues if libsodium support is not included in the release.