PTR Records and Reverse DNS
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Most marketers are familiar with DNS names that resolve to an IP address.
For instance:
extmta2-new.americanexpress.com resolves to 148.173.96.85 as you can see here:
This is known as a DNS A record, often the type of record you create in your DNS hosting provider when you want to add a domain to your website. In the email space, this is sometimes known as the "forward ".
As the postmaster of an MTA, there's another type of record you'll need to familiarize yourself with that's just as important as the A record in the email space; it's called the PTR, also known as "reverse" DNS.
In our example above, we see that extmta2-new.americanexpress.com has an A record that resolves to 148.173.96.85, but when you do a PTR lookup, you'll see 148.173.96.85 also has a DNS record, and that it resolves to extmta2-new.americanexpress.com.
The A record for extmta2-new.americanexpress.com is 148.173.96.85 and the PTR record for 148.173.96.85 is extmta2-new.americanexpress.com.
They match.
Here's why:
It's important to create your DNS records before you install Velocity MTA, add your IP addresses, and send your first test message.
When Gmail rejects your message for reasons such as bad or missing DNS records or authentication failures, if you're a first-time sender, this erroneous result may get cached, preventing you from successfully delivering a message for at least 24 hours after you've fixed the problem.
Don't risk it.
You can't set the PTR record in Cloudflare, Namecheap, GoDaddy, or anywhere you normally configure your DNS A record.
Some hosting providers allow you to configure your PTR record right in the control panel, but it's not uncommon that it can only be done by opening a ticket. This is the case with Racknerd.
See the next section Sending Domain and PTR must match for the recommended DNS configuration.
