[Pkg-exim4-users] Multihomed smarthost

[ael]

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.4
 x.y.z.5
 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
dc_smarthost='smtp.example.com::578'
 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
route_list:

smarthost:
  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
  no_more

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 :-)

ael