SharePoint VS, SMTP VS & persistence

Hello,

Hoping someone can clarify how to set up persistence with a SharePoint 2010 Virtual Server and a SMTP Virtual Server. In order to allow incoming email for SharePoint I had to set up the SMTP Virtual Server.

Do I need to set up a new persistence profile based on source address that uses the options Match across services and Match across Virtual servers or in this case, persistence is not needed?

Thanks

Susan