Asynchronous Bounces

There are three ways that an email can fail to be delivered: immediate rejection timeout asynchronous bounce Rejection A rejection is any delivery attempt where the sending smarthost can tell immediately that the mail can’t be delivered. That will often be when the receiving machine accepts a connection but returns a “hard bounce” or “5xx” error at some point in...


The term backscatter describes the email an innocent victim receives when a spammer forges the victim’s email address into a spam run. The amount of mail involved can be just a few emails or can range into the hundreds of thousands of emails. Terry Zink recently wrote an 18 part series on backscatter. It is well worth a read.

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