The keys used are:
!: modified feature, -: deleted feature, +: new feature
+1.10.0 (2018-05-19):
+
+ ! $reply_self is now respected for group-reply, even with $metoo unset.
+ ! Enabled $imap_poll_timeout when $imap_idle is set.
+ ! Added %R (number of read messages) expando for $status_format.
+ + When $change_folder_next is set, the <change-folder> function
+ mailbox suggestion will start at the next folder in your
+ "mailboxes" list, instead of starting at the first folder in the
+ list.
+ + $new_mail_command specifies a command to run after a new message is
+ received.
+ + $pgp_default_key specifies the default key-pair to use for PGP
+ operations. It will be used for both encryption and signing
+ (unless $pgp_sign_as is set). See contrib/gpg.rc.
+ ! $smime_default_key now specifies the default key-pair to use for
+ both encryption and signing S/MIME operations. See
+ contrib/smime.rc.
+ + $smime_sign_as can be used to specify a sign-only key-pair for
+ S/MIME operations.
+ - $pgp_self_encrypt_as is now deprecated, and is an alias for
+ $pgp_default_key. $smime_self_encrypt_as is also deprecated, and
+ is an alias for $smime_default_key.
+ + The <history-search> function (default: ^R) will search history based
+ on the text currently typed in. That is, type the search string first,
+ then hit ^R.
+ + The $abort_noattach quadoption controls whether to abort sending a
+ message that matches $abort_noattach_regexp and has no attachments.
+ + Mutt can now be configured --with-idn2.
+ + Unsetting $browser_abbreviate_mailboxes turns off '=' and '~'
+ shortcuts for mailbox names in the browser mailbox list.
+ ! $sort_browser now has 'count' and 'unread' options.
+ + <error-history> will display the last $error_history count of
+ error/informational messages generated.
+ + The ~M pattern matches content-type headers. Note that this
+ pattern may be slow because it reads each message in.
+ + The "echo" command can be used to display a message, for instance
+ when running a macro or sourcing a file.
+
1.9.5 (2018-04-14):
! Bug fix release.