Ok, let me make sure I have this correct. You want to use a different user account / password based on who sent the message?
Not sure how to do this with the system DSN. But, I am not strong in this area.
When I worked with Oracle, we set the user id and password in the system DSN.
As far as I knew, you set the user id and password on the send port but I didn’t think that was even used at run time.
Please keep me updated if you get it working.