strange bounce info

[Rolf Kraeuchi <rolf.kraeuchi@xxxxxxxxxxx>]

Hi

Can someone explain me the strange information in this bounce mail? 
(first recipient: Action: failed <--> Diagnostic-Code: 250)?
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Content-Description: Delivery error report
Content-Type: message/delivery-status

Reporting-MTA: dns; ns1.scnat.ch
Arrival-Date: Fri, 22 Oct 2004 08:35:36 +0200 (CEST)

Final-Recipient: rfc822; xyz@xxxxxxxxx
Action: failed
Status: 5.0.0
Diagnostic-Code: X-Postfix; host idoor.zg.ch[212.4.70.45] said: 250
    <xyz@xxxxxxxxx>, Recipient ok (in reply to DATA command)

Final-Recipient: rfc822; abc@xxxxxx
Action: failed
Status: 5.0.0
Diagnostic-Code: X-Postfix; host kaya.wsl.ch[193.134.202.7] said: 550 
Not a valid WSL address (in reply to RCPT TO command)
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cheers,
rolf