[exim] verify = helo, PTR record lookup

Hello exim-users@???,

>From the docs of the verify = helo operation
it appears that this check succeeds if

A) the HELO string is an IP literal that matches $sender_host_address
[127.0.0.1]

OR

B) the HELO string is a name can be resolved to the
$sender_host_address

OR

C) the $sender_host_address can be reverse-resolved to the HELO string
(PTR record lookup)


A, B work as intended, but C somehow does not (at least not if the PTR
record resolves to a name that has no A/CNAME entry itself, or the name
does but points to a different IP)

Any hints on what the problem is here?

My ACL RCPT check looks like the following:

  warn   !authenticated    = *
         verify            = helo
         set acl_m_helorfc = true

Also, as I can see from the code, if verify=helo runs into
temporary DNS problems, it fails rather than creates a
defer, unlike most other DNS related checkers in Exim,
could somebody confirm this please?