Neil wrote:
At what point does the "Sender: " header usually get added to the mail?
it's added by the sender.
Because some (and so far the only pattern is "It shows up when subscribing to the SpamAssassin Mailing List.") of my mails at getting that header attached (and with a bad address) and it's annoying me...
what do you exactly mean? almost all mailing lists set this header and "we" have no problem with that. if you are annoyed by the "on behalf of...", replace your mail server(s) and/or mail user agents with ones that don't annoy you...
