[CentOS] sendmail mail relay backscatter issue.

Simon Billis simon at houxou.com
Thu Feb 4 13:28:04 UTC 2010

Hi Folks,

I have a couple of questions which I hope that you will be able to assist
with, first some background.

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.

I currently use /etc/mail/access.db as the access map for the domains, but
this allows all mail to be accepted for the domain before the attempting to
send it on for final delivery which causes NDR and backscatter for those
domains which do not have a catch-all account.

I have looked at adding "To:user at domain RELAY" to the access map and also
adding "define(`_RELAY_FULL_ADDR_', `1') " in the sendmail.mc and running
make -C /etc/mail but this has no effect on the sendmail.cf file. My
understanding is that if I can get sendmail to accept this undocumented
feature then all will be fine as I will be able to use the access map to
allow mail to those specific users as well as entries of the type "domain

My first question is: Does anyone have any ideas as to why I wouldn't be
able to have this change reflected in sendmail.cf?

My second question is: Does anyone have any ideas on how to utilise access
map and relay-domains to achieve the same thing?

Thanks for your time and assistance.


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