Hi Martin Husemann, you wrote:

> To be precise, the mailer I'll have to deliver mail to says (as only relevant
> line in response to EHLO):
> 
> 250-AUTH PLAIN LOGIN

I had the same problem a few weeks ago. My solution was qmail.

Qmail doesn't support authentication out of the box and most of the patches
available for SMTP AUTH assume qmail as the receiving MTA, i.e. the one
evaluating the password sent by the client.

The only exception I could find didn't work for me from the start
(don't remember the problem anymore). After some fiddling with the patch
I can now use AUTH PLAIN and AUTH LOGIN with my upstream MTA.
I haven't found the time yet to apply this solution to the serialmail
package (an add-on for qmail) as well, which would be far more
appropriate for my situation...

If you're interested, I can make the patches available to you.

ciao
     Klaus