What does Failed; 4.4.7 (delivery time expired) mean?
If you receive an email from postmaster with the error message:
Failed; 4.4.7 (delivery time expired)
This means that a message was sent from your address and did not make it to the destination address before the time limit expired. There may be a network outage between the source and destination networks.
If you sent the message quoted in the mail, check the address and try sending again later.
If you did not send the message quoted in the mail, then another person may have sent the message using your address in the 'from' field.
Note: You can test for problems sending to a particular address using the tools at http://www.dnsstuff.com