Does Mautic handle errors from relay mailserver?

We tried to use our own SMTP mailserver for sending out newsletters but found that if this gave back some STMP errors like “554 5.5.1 Error: no valid recipients” that Mautic don’t handle these messages, besides of putting it into the logs.
We now added another SMTP server as intermediate transporter (running postfix on local host of Mautic webserver) and it works.