Gut the Session interface

internal/smtp/msa.go

@@ -60,13 +60,13 @@ func (m *msa) Login(user, pass string) (smtp.User, error) {
 		return nil, fmt.Errorf("Login failed")
 	}
 
+	sid := atomic.AddUint64(&m.sid, uint64(1))
 	session := &Session{
-		ID:      atomic.AddUint64(&m.sid, uint64(1)),
-		Account: account,
-		Handler: &Sender{},
+		ID:      fmt.Sprintf("submission:%d", sid),
+		Handler: &sender{msa: m, account: account},
 	}
 
-	log.Printf("Beginning submission session %d for %s", session.ID, user)
+	log.Printf("Beginning session %d for username=%s", session.ID, account.Username)
 	// FIXME: TODO: Track ongoing sessions for termination or notifications
 
 	return session, nil