fix journalctl postfix command

tests/test_email.py

@@ -145,7 +145,7 @@ def check_send_test_email(conf: dict) -> int:
         cmd = "grep '{}' /var/log/mail.log".format(email)
     else:
         u.info("/var/log/mail.log not found, trying journalctl")
-        cmd = "journalctl -u postfix | grep {}".format(email)
+        cmd = "journalctl -t postfix/smtp | grep {}".format(email)
 
     # logs polling
     time.sleep(1)