[Cel] Undelivered Mail Returned to Sender

This is the mail system at host smtp.agh.edu.pl.

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

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

The mail system

woznyk@agh.edu.pl: host poczta.agh.edu.pl[149.156.98.98] said: 550 5.1.1 woznyk@agh.edu.pl: Recipient address rejected: User unknown in virtual mailbox table (in reply to RCPT TO command)