Multiple A records and reverse DNS
schulz at adi.com
Tue Mar 22 15:28:03 UTC 2016
> Tom, when your mail server establishes a connection to another host, the
> receiving host will likely automatically check the PTR record of the IP
> address your server used as it's source address. This PTR record should
> have a corresponding A record that points to the same IP address that
> was looked up in the PTR record. This is sometimes referred to as a
> "verified" hostname. Without this, receiving mail servers may sometimes
> log your rDNS as unknown, which can look spammy to subsequent spam
> filters. You can have any number of other A records that point to your
> server, they are irrelevant to PTR verification.
> Your reverse zone:
> 126.96.36.199.in-addr.arpa. IN PTR mail.adi.com.
> Your adi.com zone:
> mail.adi.com. IN A 188.8.131.52
> smtp.adi.com. IN A 184.108.40.206
> www.adi.com. IN A 220.127.116.11
> foo.adi.com. IN CNAME www.adi.com.
> All the matters to PTR verification is that 18.104.22.168 has a PTR record and
> that PTR record exists as an A or CNAME that eventually points back to
> As others have pointed out, this is best common practice for outgoing
> mail servers aka mail relays; However, I generally recommend having
> valid PTR records and having matching forward records for any servers.
> Maybe it's just me, but most of my server's send email - even MX servers
> (they do create NDR notices from time to time).
That is mostly how I thought it worked. What I had in mind more
mackerel.adi.com. IN A 22.214.171.124
mackerel.adi.com. IN A 126.96.36.199
188.8.131.52.in-addr.arpa. IN PTR mackerel.adi.com
184.108.40.206.in-addr.arpa. (not yet set up)
With mail going out on only 220.127.116.11 but receiving mail on both.
But receiving mail on both was more work than I had expected, so I am
not going to set that up. When reverse for 18.104.22.168 is finally set
up I will just do a late night switch over.
> Thomas Schulz wrote on 3/17/2016 8:53 AM:
> > This is not a BIND question but I hope people here will know the answer.
> > We are switching service providers and I understand that many email SPAM
> > prevention systems insist on the reverse DNS matching the forward DNS.
> > If I have two A records for our mail server and the reverse record matches
> > one of them, will that be good enough. Or will the fact that the other A
> > record does not match cause trouble.
Applied Dynamics Intl.
schulz at adi.com
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