forwarded messages OM/Exchange change sender address

[Jamie Harre]

An Exchange user sends a message to a second Exchange user. This user forwards
the message to an Openmail user. The Openmail user gets the forwarded message,
but it has the second Exchange user's address as the sender.
In my tests, it shows an "on behalf of" situation: that is, the address would
be forwarding-user's-address on behalf of original-sender's-address.

In all these cases, Outlook is set up with "When forwarding a message, attach
original message".

[Kasper Haitsma]

I do not see your question. If someone forwards a message, [s]he becomes the sender of that message (the fact that another message is attached is not really relevant) For OpenMail, Exchange and even sendmail, this is a new message, and therefor it makes sense to display the creator as the sender.
You did not state if the message is forwarded manually, or automatically (by means of a rule) still your 2nd Exchange user is the creator of the forwarded message, and will be displayed as the originator. Now with OMGui you had the choice, when forwarding automaticlly, to retain the original sender. This is an OpenMail feature, not a common standard. The "on-behalf-off" has to do with designates. If user2 is a designate of user1 (is allowed to manipulate user1's mailbox, using his[her] own logon), user2 can send "on-behalf-off" user1. User2 will be the creator, but replies will be sent to user1. This information is usually lost, after the message is transfered through the SMTP gateway (OpenMail)/SMTP connector (Exchange).

HTH
Kasper