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Mail Tester
Understanding MX Records, PTR Records, and Reverse PTR Records AKA rDNS


Where does your emails come from? That's the important question that so many different email authentication and validation techniques depends on. In your email headers as previous discused here: Email Headers. We are going to focus on the most recent "Received" and the MX records listed under the "From" (5321) header and the "return-path" (5322) headers.
 
Under the latest "Received" header - it contains the mail server name and IP that sent the email to the final destination. This is also known as the LSIP address or Last Sending Ip Address. This IP addresses is used to validate your SPF record against. It is also VERY important that the LSIP has a reverse PTR Records set up that points back to the domain name of the mailserver that sent the email. If this rDNS record is missing, you have a very good chance that the email will be marked as spam. If your rDNS points to a generic name or some other place, it can be flagged as spam. We also test for this condition and mark it as critical.

Mail Tester will also test MX records found under both the 5321.From and 5322.From domains, this can be the same as the LSIP. In any event all your MX Records should have an rDNS record, but it's super critical that your LSIP has one. If any rDNS is missing for any MX or LSIP, Mail tester will flag this as a critical error. If you're using gmail or hotmail to send, some of their incoming MX records don't have rDNS records set up. But their out-going mail server IP's do.  Most smaller companies incoming MX record IPs are the same as there out-going Mail IP's, when it comes to sending mail, this is why we flag this condition as critical. It's up to you to make the determination, if you need to set up a PTR record, based on the information provided here.

It's also important that you only have 1 PTR record per IP, having more then 1 PTR will cause issues in email delivery, we also flag this condition as critical.
 
Read out next blog in the Mail Tester Series: Mail Tester - RFC Syntax Checking

The Mail Tester Pro Report

MX Records
Pref Value Blacklists
0 mail.unlocktheinbox.com Check For Blacklists

rDNS PTR Records
Records Results
Domain:mail.unlocktheinbox.com
- Type:MX
- IP Address:168.144.32.36
- ARPA Record:36.32.144.168.in-addr.arpa.
- rDNS PTR Record:mail.unlocktheinbox.com
- rDNS PTR Test:Passed
- RDNS PTR Count:

1 Found - Passed

Domain:unlocktheinbox.com
- Type:LSIP
- IP Address:168.144.32.46
- ARPA Record:46.32.144.168.in-addr.arpa.
- rDNS PTR Record:unlocktheinbox.com
- rDNS PTR Test:Passed
- RDNS PTR Count:1 Found - Passed
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