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Phantom Email Returns

Posted on 2009-05-08
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Last Modified: 2013-11-30
Occassionally I get non-deliverable notifications of emails that I did not send OR that are addressed to a bogus mailbox in my domain.  My SMTP is NOT an open relay.  Is this the result of a failed attempt to relay or is this something I should be concerned about?

THanks~
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Question by:Bob Schneider
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2 Comments
 
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by:Stacy Spear
Stacy Spear earned 400 total points
ID: 24336623
Spammers at work, as long as the server reporting the NDR isn't yours, you are good.
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Chris Dent earned 1600 total points
ID: 24336680

It's called Backscatter, and generally caused by someone (a spammer) spoofing e-mail addresses (they send as your address / domain). The trouble is it's really really easy to do that, SMTP is really rather insecure.

You can help with this to an extent by implementing an SPF record for your domain. That allows you to state which servers are allowed to send mail as your domain name. It will only help to an extent though, not everyone checks the record, and if they don't they have no way of telling a message is spoofed.

There are wizards to help you make SPF records here:

http://www.openspf.org/

And here:

http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/

If you happen to be using Exchange 2007 it is also possible to construct Transport Rules which can tag outbound mail to prevent Backscatter. Then further rules can be configured to drop Inbound Non-Delivery Reports unless the tag is included (which it would be if the message header).

Chris
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