- this method isn't as deprecated as IMAP LOGIN;
- it allows to keep hashed passwords on the server side;
- it has the ability to specify that the remote identity
is different from authenticating username, so it even
can be useful in some cases (e.g., migrated mailboxes);
configuration variable "remote_identity" was introduced
to leverage this functionality.
From: Andreas Mack <andreas.mack@konsec.com>
Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>