[Pkg-exim4-users] Multihomed smarthost

ael law_ence.dev at ntlworld.com
Mon Dec 23 10:06:54 UTC 2013

My smarthost is multihomed: dns lookup replies with a list of addresses
none of which matches the "collective address".

So looking up smpt.example.com yields
 x.y.z.6  etc.

Reverse dns on these addresses gives smtp1.example.com,smtp2.example.com
and so on.  This is a very common way of spreading load and adding
resilience, I think.

However, setting
 in update-exim.conf.conf
fails the reverse dns test - which is perhaps not very surprising. 

I could find nothing about this is the debian documentation nor in the
searches around exim in general, but maybe I was missing a key phrase.

I see that dc_smarthost is used to set the macro DCsmarthost and that in
turn is used (in my situation) only in the smarthost router in the

  debug_print = "R: smarthost for $local_part@$domain"
  driver = manualroute
  domains = ! +local_domains
  transport = remote_smtp_smarthost
  route_list = * DCsmarthost byname
  host_find_failed = ignore
  same_domain_copy_routing = yes

Consulting spec.txt.gz, it seemed that I could use a list:
"This is so that they may contain colon-separated host lists"

I did try 
dc_smarthost='</ smtp0.example.com::587/smtp0.example.com::587/smtp2.example.com::5870'
but that resulted in:
error in router: unknown routing option or transport name

Perhaps I should be using host_randomize, but that would need a
modification of the standard Debian template.

It will be apparent that I am a novice in exim. Currently I work around
by simply using a single smtpx.example.com.

Can someone help? This must surely be a very common situation, yet I
couldn't find a solution. I suppose when I have read and fully
understood the spec several times, it may become obvious, but that is a
daunting task :-)


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