Leander S. wrote:

Am 23.07.10 02:59, schrieb Andrew Bruce:

...

eel free to post this to the running conversation on the list (strip my email address from this email though please) The issue was a case sensitive typo. When Setting up your Thunderbird don't type in eMail Addresses & Usernames including uppercase letters!

DON'T: User@Domain.tld BUT therefore: user@domain.tld

Better, when checking for valid recipients, always lowercase the input befopre doing so.

Dovecot uses %Lu (the 'L' means 'lowercase')...

I faced that Problem only when I was using dyndns as domain service provider.

Dunno about dyndns, but usernames should never be case-sensitive, passwords always.