You haven’t mentioned what e-mail solution (ICS 6.5 or Multimedia/eServices 7.x/8.x) your customer has but I will assume Multimedia/eServices. In this case you would need to check value of ‘Mailbox’ key stored in interaction’s UserData and set priority based on that. Value of this key matches to value of the ‘address’ option defined for particular email account in Email Server Java options (pop-client section).