Backscatter solutions

[Jorey Bump]

Ian Eiloart wrote, at 05/09/2008 05:54 AM:

> If you aren't using SPF, then you can't really complain about backscatter. 
> If you deploy SPF, then you can expect a bit less backscatter, and you can 
> encourage others to check your SPF records.

Backscatter is created when an MTA accepts a message that it can't relay 
or deliver, thus generating a bounce to the (alleged) sender. I fail to 
see how SPF (or just about any other check) can eliminate backscatter if 
it's not applied at the first MTA in the chain, rejecting the message 
during the SMTP transaction. After that, the game is mostly over, 
because the original connection has completed, and a bounce will be 
generated in the case of nondelivery.

Ideally, MTAs shouldn't accept messages that can't be delivered, for 
whatever reason. How this is dealt with depends on the MTA's role in the 
process. Aside from the traditional sender's submission MTA and the 
recipient's destination MX, there may be intermediate MTAs that 
complicate the process (gateways, third party filtering services, poorly 
configured final mail stores, etc.). I suspect that it is the 
proliferation of these that are responsible for the sudden surge in 
backscatter, not any changes in behaviour on the part of spammers. Email 
administration is complicated, and the trend has been to outsource this 
headache to anyone who will take your money, regardless of whether or 
not they follow best practices.

In any case, by the time it gets to your IMAP server, there isn't much 
you can do about it other than sort it into folders or delete it.