[CentOS] sendmail mail relay backscatter issue.

Simon Billis simon at houxou.com
Thu Feb 4 15:02:07 UTC 2010

> One approach here if it is practical to collect/maintain all of the
> valid
> recipient addresses is to build a virtuser table with a default reject
> for each
> domain the relay handles plus the list of all valid addresses.  This is
> very
> efficient if you can automate the table updates or the user base is
> stable.

I have already written the code that updates the access file and the
relay-domains file from the final delivery mail server so I think that to
create a virtusertable should be simple enough, I'll check the documentation
to see how to use the virtusertable in this manner - thanks for the pointer.

> Another would be to use MimeDefang as the framework instead of
> mailscanner.  It
> has an option to check recipient addresses via smtp to the delivery
> servers
> before accepting.  You may have to write a snippet of perl to get that
> right for
> multiple domains (that's a feature...).  This is less efficient but
> works in
> real time against the addresses that will be accepted for delivery.

I'm not so sure that this is an acceptable overhead - the mail scanners
process 2,000,000 messages a day.



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