If domain.de is an external domain then you should not have it listed in "Local Domains".

You can set a local user for each MercD pop account to deliver to, or set an alias for the you@domain.de address (or get your own domain name [:)])

I use the MercuryD and MercuryC protocol.

The Problem:

User Peter is outside, (peter@domain.de) and he reads his mail with a webmail online.

The other user are inside (e.g.: Paul@domain.de). Now Paul write an email to peter@domain.de and Mercury think Peter is an local user and answer:

"The local mail transport system has reported the following problems
it encountered while trying to deliver your message:

-------------------------------------------------------------------
*** peter@domain.de
User peter@domain.de not known at this site.

Mercury should send this mail via MercuryC to my ISP.

What can I do?