So VSNL has sent a clarification mail to all subscribers. The question now for us linux users is how to configure sendmail/postfix/exim/etc to set the MAIL FROM: as blah@vsnl.net while still keeping the From: as whatever we want?

Editing the source is one option, but one I'd like to avoid as far as possible. Is there a configuration directive/pipe through procmail that can do it?

If you don't want to go through this hassle though, the easiest way is to set a Reply-To: header. This may mess up with mailing lists though, like this one.

Philip