This was discussed in this recently closed thread http://www.userscape.com/helpdesk/index.php?pg=forums.posts&id=6752&pc=7
I have tried “everything” to get this working right down to entering the data - as outlined in the thread above - manually at the start of an email and then sending in plain text so as if recreating a forwarded message - but each time it picks up the sender and not the forwarding part.
Is there anything else that could be stopping this working?
In case it matters this testing was done using Thunderbird.
One suggestion for poster in the earlier thread is that they could try - and it should work - setting up another email account - within their email client - that is for the address that is normally forwarded to. The drag the email across to this account where it will be picked up and the from address will be that of the sender.
If a POP3 account then the email client needs to be set up so that it does not POP emails from the account.
I have only tried it with Thunderbird and IMAP and with a different program but it worked fine.