[CentOS] sendmail mail relay backscatter issue.

m.roth at 5-cent.us m.roth at 5-cent.us
Thu Feb 4 14:24:17 UTC 2010

Mike wrote:
> Simon Billis wrote:
>> I run a few sendmail servers that run MailScanner/Spamassassin/sendmail
>> (current versions) on Centos 5.4 and Centos 4.8 These boxes accept mail
>> for a large number of domains (6000+) scan the mail removing spam and
>> then forward the ham to another server for delivery. I am attempting to
>> stop any backscatter that these servers cause by only accepting mail for
>> specific users at domain or for domains with a catch-all account.
>> running
>> make -C /etc/mail but this has no effect on the sendmail.cf file. My

Does it not give output? Have you tried adding -d?
> 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 would question how "real time" that would be for every email for 6k+
domains. If a few have a large client base, or are expecting responses
from a mass emailing, it might start to take a *while*, unless you've got
pretty heavy duty equipment and networking.


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