Google Cloud DNS迁移后邮件服务器反向DNS（PTR）问题求助

Let’s break down your problem step by step—reverse DNS can be tricky because it operates under rules that are easy to mix up with regular domain DNS.

First, a Critical Clarification #

Reverse DNS (PTR records) has nothing to do with your domain’s authoritative DNS servers (even though you’ve pointed GoDaddy to Google Cloud DNS). PTR records live in a separate, dedicated DNS zone controlled entirely by the owner of your mail server’s IP address—in your case, your original hosting provider. When a mail server checks your PTR record, it doesn’t look at Google Cloud DNS; it queries the DNS servers assigned to the IP block your mail server uses, which are managed by your old host.

Why MXToolbox/DNSStuff Are Showing "No PTR Record" #

Even if your old host claims they set up the PTR, there are a few common reasons it’s not showing up in tests:

• Incorrect PTR configuration: They might have mapped the wrong IP to mail.inspireddev.com, or typed the domain name incorrectly (e.g., missing a .com, extra spaces, typos). Double-check that the PTR record points exactly to your mail server’s fully qualified domain name (FQDN).
• Unpublished reverse zone changes: Your host might have added the PTR record but failed to update the authoritative name servers for the reverse IP zone, or the changes haven’t propagated to global DNS root servers (reverse DNS TTLs are often set to 24 hours or longer).
• Tool caching: Some DNS testing tools cache results aggressively. Even if you’ve waited what feels like long enough, manual checks can bypass this cache to get accurate results.

Step-by-Step Fixes for mail.inspireddev.com #

1. Manually verify the PTR record
   Open your terminal and run either of these commands (replace <YOUR_MAIL_SERVER_IP> with the actual IP of mail.inspireddev.com):

   dig -x <YOUR_MAIL_SERVER_IP>
   # Or
   nslookup <YOUR_MAIL_SERVER_IP>
   

   If the output doesn’t return mail.inspireddev.com, your host definitely messed up the setup. Send them the output and ask them to correct it immediately.

2. Confirm the reverse zone’s authoritative servers
   To ensure reverse DNS queries are routing to your host’s servers, run this command (adjust the IP segment to match your mail server’s IP—e.g., for IP 123.45.67.89, use 67.45.123.in-addr.arpa):

   dig -t NS <IP_SEGMENT>.in-addr.arpa
   

   The result should list your original host’s DNS servers. If not, your host doesn’t control the reverse zone for that IP block (unlikely, but possible)—escalate with their support to fix this.

3. Escalate with your original host
   Provide them with:

   • The exact IP of mail.inspireddev.com
   • The exact FQDN the PTR should point to (mail.inspireddev.com)
   • The output of your manual dig/nslookup commands
     Ask them to confirm the PTR record is correctly added to the reverse zone, and that the zone’s NS records are properly published to the global DNS system.

4. If you want to fully escape your old host
   The only way to take full control of your PTR record is to move your mail server to a provider that lets you manage reverse DNS for their IPs—like Google Cloud. If you spin up a Compute Engine instance in GCP and assign it an IP for your mail server, you can create the PTR record directly in Google Cloud DNS and never have to rely on your old host again.

内容的提问来源于stack exchange，提问作者Tony