Grrr...Flickr says:

This is the Postfix program at host www4.

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

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

The Postfix program

: Name service error for name=www4.www4 type=A: Host not
found


Final-Recipient: rfc822; photos@www4.www4
Action: failed
Status: 5.0.0
Diagnostic-Code: X-Postfix; Name service error for name=www4.www4 type=A: Host
not found