Problem z pošiljanjem maila k eni osebi

This is the Postfix program at host www1.email.si.

I'm sorry to have to inform you that the message returned
below could not be delivered to one or more destinations.

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 message returned below.

The Postfix program

obrul.ivan@siol.net: host mailhub.siol.net[ 193.189.160.25] said: 550 Invalid
recipient: obrul.ivan@siol.net (in reply to RCPT TO command)

Final-Recipient: rfc822; obrul.ivan@siol.net
Action: failed
Status: 5.0.0
Diagnostic-Code: X-Postfix; host mailhub.siol.net [193.189.160.25] said: 550
Invalid recipient: obrul.ivan@siol.net (in reply to RCPT TO command)

V čem je problem in kako naj kontaktiram osebo, kateri pišem mail?

Na tega ivana naj bi poslal mail z napako. Drugače pa pošiljam (če smo točni ODGOVARJAM) na mail spjker@email.si