Hi Danish,
Rather than toggling the users for the incoming and outgoing profile for Outlook and Email router, A recommended practice for large deployments and such cases in which you want to differentiate the campaign sender would be to use a dedicated profile (set it first in the router as incoming and outgoing) and add only that particular user it. You may disable other users for that profile as CRM would load all the mailboxes for a particular profile.
Sumit is right in suggesting "create a new outgoing profile with different SMTP Provider and can disable the existing SMTP profile."
I am not sure how you have changed the POP3 setup from the ABC to the XYZ provider from the application itself as this is set int the Email Router.