The problem is that that the "other side" does sender address verification using the header sender ("From:" header). This is incompatible with BATV, and also with some mailing list implementations and some "robot" email. They should use the envelope sender instead.

You should be able to create an exception for BATV using a *@theirdomain.com mask entry, instead of turning it off entirely.

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Tom Kistner
Product Development & Administrator
Astaro AG