Similar to WHMCS (docs.whmcs.com/Email_Importing),
Clientexec (clientexec.com/members/knowledge-base/configuring-clientexec~82/email-routing~437)
or Hostbill (hostbillapp.com/feature/support-ticketing-system-overview/#import)

This would also allow the mail server to be on a different server than wisecp.