[exim] Backup MX on Primary UP -> reject

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Author: pisang
Date:  
To: exim-users
Subject: [exim] Backup MX on Primary UP -> reject
I have debian with Exim 4.50-8sarg running as a backup
MX so I added my dc_relay_domains in de config

1) How many dc_relay_domains can I put in this config
? I'm not using the split config and its getting long.

2) I do not wish to discuss the need / or not of a
backup MX. I want to run one but I want the following.

When a message is recieved Exim checks if the primary
mail server for the recipient domain is up. If its up
it deny's the message.
Only when the recipient domain / primary mail server
is down the message gets queued and relayed when the
primary mail server is back up.

I have tested this with ACL.

deny
domains = +relay_to_domains
verify = recipient/callout=1000s,nocache
message = Primary MX for $domain is up, please try
that.

It only works without the nocache. but then my accept
doesnt work since the recipient lookup is cached and
it deny's the message.

Is there a way to use verify = to check if the primary
mx can reply's to ping ? =up&running

-------
I want the behavor of Milter-ahead for sendmail
http://www.snertsoft.com/sendmail/milter-ahead/index.shtml

-primary-up-reject
We are a backup MX and we want to reject mail when the
primary MX is available. This does not conform with
RFC 974 & 2821 mail routing, which only requires mail
clients attempt delivery to the primary first, before
trying other MXes.
Spammers often attempt to by-pass spam filters by
sending email directly to secondary MX machines, which
often have weaker requirements. This option
essentially demands that a client only deliver to the
primary MX when it is available.




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