>Reliably matching up the PTR to the "A" record is virtually impossible.
You create the problem with multiple PTRs per IP, so you can fix it by
using the best practice of only one PTR per IP.
Forgetting about the virtual elements, I think its's usefully simplifying
to think of "canonical" PTR + A records for a non-virtual domain.tld used
in those two DNS records and repeated in SMTP setting as the SMTP-greeting
and HELO domain name. The ephemeral virtuals can come and go, but the
following 4 settings remain fixed:
d.c.b.a.in-addr.arpa. PTR label.can_domain.tld.
label.can_domain.tld. A a.b.c.d
HELO label.can_domain.tld
220 label.can_domain.tld
The above setting have no relationship or dependency on envelope sender or
recipient domains that transit the MTA at that IP, not any relationship
with any MX records.
Len
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