[StAPF] Delivery Status Notification (Failure)

The following message to <gebhardt(a)cvjm-hochschule.de&gt; was undeliverable. The reason for the problem: 5.1.0 - Unknown address error 550-'5.7.23 <gebhardt(a)cvjm-hochschule.de&gt;: Recipient address rejected: Message rejected due to: SPF fail - not authorized. Please see http://www.openspf.net/Why?s=mfrom;id=stapf@zapf.in;ip=129.206.100.212;r=...