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Feature request: smtpchk additional output check

Posted by Stu M 
Stu M
Feature request: smtpchk additional output check
February 09, 2018 11:10AM

I have a small but hopefully simple request that would be useful in
Exchange SMTP load balancing situations.

When Exchange 2013+ hub transport service is put into maintenance mode it
keeps the SMTP service running but responds to mail from commands with "421
4.3.2 Service not active" - I believe this is for "smart redirect" of
Outlook clients that can relay thru another server in a cluster.

However, where other MTAs are concerned, when relaying thru a load balanced
Exchange this becomes problematic because they simply fail to submit
messages - HAproxy still sees the backend server is up because SMTP is
still alive, despite using smtpchk (Exchange still responds to the ehlo
command, see below).

E.g. typical output when a hub transport host is in service mode..

220 xyzserver Microsoft ESMTP MAIL Service ready at Fri, 9 Feb 2018
09:32:20 +0000
250-xyzserver Hello [x.x.x.x]
250-SIZE 37748736
mail from: me@hotmail.com
421 4.3.2 Service not active

My question is, would it be possible to have add additional option for
smtpchk that causes HAP to look for additional data in the SMTP response -
specifically the last line above "service not active"?

So after doing ehlo, if HAP then does a dummy "mail from:" it will get the
result code at that point, perhaps something like the following would

option smtpchk ehlo <somedomain>
option smtpchk-exch <sender-address>

Appreciate any thoughts on this.

Best regards,
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