Für die IMAP-Anmeldung scheint die UMA nur das optionale und unübliche Verfahren AUTHENTICATE PLAIN zu verwenden.
Standard ist jedoch AUTH LOGIN.
Dieses Verhalten zwingt und stattdessen POP3 zu verwenden, wodurch wir andere Nachteile haben.
Hier dazu ein Auszug aus einem Service-Ticket unseres Mailserver-Anbieters:
> we have an email archiving system which should connect to VPOP3 using IMAP.
> Unfortunately this fails, because of a login type mismatch.
> The support told us, the problem is VPOP3 does not advertise the plaintext login method in the capabilities.
> Then the appliance tries to announce the login method with AUTHENTICATE PLAIN, but this fails.
That is very strange behaviour by your archiving software. VPOP3 supports plain text login using the standard 'LOGIN' command. 'AUTHENTICATE PLAIN' is an optional alternative plain text authentication method that almost no one uses, because the standard 'LOGIN' command is always available, and it does the same thing.
So, I don't understand why your archiving software would want to use the optional extension 'AUTHENTICATE PLAIN' when 'LOGIN' does the same thing and is a standard part of IMAP4.
I think you need to report it as a bug to the archiving software support. Requiring an optional extension when a standard feature does exactly the same thing is not normal.
(Also, the archiving software sending the "AUTHENTICATE PLAIN" command when the server has not said that it is supported is a bug as well)