This is the mail system at host owncloud.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<test@niepodam.pl> (expanded from <root>): host niepodam.pl[178.32.206.243]
said: 550-Verification failed for <root@owncloud> 550-Unrouteable address
550 Sender verify failed (in reply to RCPT TO command)