(Ted Harding) Ted.Harding@nessie.mcc.ac.uk writes:
I want to find a way to *force* sendmail to include a specified "Return-Path:" header in mail it sends to a remote [E]SMTP server.
No, you don't. Return-Path is only added at final delivery.
Specifically:
Return-Path: Ted.Harding@nessie.mcc.ac.uk
rather than the header it computes automatically.
What you actually want is probably the -f option to sendmail (and its workalikes).