Hi, 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 EHLO 250-xyzserver Hello [x.x.x.x] 250-SIZE 37748736 250-PIPELINING 250-DSN 250-ENHANCEDSTATUSCODES 250-STARTTLS 250-8BITMIME 250-BINARYMIME 250 CHUNKING mail from: m...@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 suffice? option smtpchk ehlo <somedomain> option smtpchk-exch <sender-address> Appreciate any thoughts on this. Best regards, Stuart.
