Hey, thanks for your lines! I tried it, but it helps me not.
If I guess it right, than this parameter "zimbraPop3CleartextLoginEnabled" is for users using the POP3 feature of the zimbra server and connect to their mailbox (on the zimbra server!) via pop3 protokoll - and not for an external pop3 account (like @yahoo and so on).
I'm a bit confused, that I ve no troubles creating an external account with my first installation (ubuntu 8.0.4 / 32Bbit) and now with debian 5 / 64 bit - it wont work!
Are there other hints to check out, where the error was living?
Tim