Default domain in outgoing email?

[Stefan Monnier]

A lot of the email messages I send go to addresses @iro.umontreal.ca.
And when I send them from my office machine, this address is automatically
added by the `postfix' mailer.  But from my home machine, this is not the
case (for various reasons it is not practical to change my `postfix' mailer
to do this rewrite on those machines).

So, I'd like to add this domain automatically directly from Gnus.  I looked
briefly at message.el but couldn't find any configuration for this feature.
So do I need to write some elisp code for it?

If so, can someone tell where to start?  Which hook would be best and what
functions could I use to loop through the relevant header field(s) and what
functions can I use to loop through each email address on each header field?


        Stefan