[user_external] imap: username and username@domain.com are treated as different users

[yennor]

Affected apps

user_external plugin, using imap authentication

Expected behaviour

if you use an imap server which accepts logins with or without domainname, when a user logs in as
"user" or
"user@example.com" it should be treated as the same logins.
There should somehow be a possibility to tell the plugin to, either, always add the domain if the user didn't add it, or to strip the domain from the username if added.

Actual behaviour

An account "user" and a different user "user@example.com" are created..

[crysman]

this affects me, too, it is very annoying
related issue: #2223

[crysman]

any progress might be expected here?