Deliver Warning:

The first important point is to examine the ‘Subject’ of the message you received, if it starts

“Delivery Warning…”

Then you can safely ignore the message, this warning only means the ‘first’ attempt to send to the specified address failed, it’s likely further attempts will work. However the warning is useful if the message is ‘time critical’ you can take steps (make a phone call, send a fax) immediately to make sure your ‘message’ gets through.

The rest of the bounce message is in a standard and slightly obscure format, intended to be read by both humans and robots, the key line to examine is this one:

For EMAIL@DOMAIN.NAME, REASON

That will tell you the address the mail server was trying to deliver the message to, and the reason it failed.

Click here for a list of specific bounce explanations