[Mimedefang] backup MX server & checking for valid users

alan premselaar alien at 12inch.com
Tue May 13 23:12:02 EDT 2003


I could have sworn someone posted something to the list related to this, but
i can't for the life of me find it in my archives.

it may be slightly off topic, and if so i appologize in advance.

I'm running MD 2.33 and SA 2.53 on my primary and secondary MX servers.

the scenario i have right now is:

on my LAN I've got an Exchange server
on the DMZ I have my primary MX server which does LDAP lookups to the active
directory to reject uknown users at SMTP negotiation time. (so that way my
postmaster mail doesn't get slammed with a bunch of "can't deliver to this
non-existant email address" emails because of all the bunk virus/spam mails.

this is working really well.

at a different location, on a public network, I have my backup MX server
which is also running MD 2.33 and SA 2.53.  It's setup to forward all mail
(after scanning) to my primary MX machine.  So far it works pretty nicely
except that, if a spammer targets my secondary MX machine to try to deliver
mail to an unknown user here, then my primary MX server rejects it back to
the backup server, which ques the mail to goto the sender who doesn't exist
and eventually fillls up my postmaster mailbox with the "can't deliver
message" emails.

is there any way to configure sendmail and/or MD to do an SMTP user_exists
type of check from the secondary MX server to the primary MX server? (making
the assumption that if the primary MX server doesn't respond in $TIMEOUT
that the mail will be accepted and queued) ?

if there is, would it be an MD filter routine? or something sendmail can be
configured for?

as usual, any and all assistance is greatly appreciated

alan




More information about the MIMEDefang mailing list