[exim] Checking if a list of domains contains a domain conta…

I don't know if this check can be accomplished in Exim at all - but here
it goes. I need to know if any of the results of a dnsdb lookup which
returns multiple records exists in a predefined dnslist. I'm guessing
this is not really possible, I just thought I'd check.

To expand a bit, I need to know if any of the MX servers of a domain
exists in a dnslist of whitelisted domains. The code below works fine if
the dnsdb MX query returns only one record, but obviously doesn't work
if there are multiple MX records:


domainlist no_extended_callout_mxs = *.fussy_mx1.com : *.fussy_mx2.com

condition = ${if match_domain {${lookup
dnsdb{mx=$sender_address_domain}}}{+no_extended_callout_mxs}}


For example the mx query might return:

10 mx1.exampledomain.com
20 mx2.exampledomain.com
0 exampledomain-com.mail.protection.outlook.com


For example I'm interested in the *.outlook.com domain - I want to know
if it is in the list of mx's - but I am essentially comparing a list
(the list of mx records) with another list (of whitelisted domains)-
which I guess is not possible.

I can't do a straight comparison using the $sender_address_domain, as I
am trying to whitelist domains which use mx's of certain hosting
platforms (such as those hosted on various MS cloud platforms) - which
are really fussy about extended callout verfication (but a major source
of spam at the same time, ironically!)