Dhanamerdeka
Hello, find a server provider or network provider to make a PTR record for your ip.
What is your system like? debian11 has not yet adapted to the mail server

    Solution for all this is....

    • Check port 25 (on my case, the port is opened but by vps operator it's open as "filtered") so we need to fully open it....
    • add PTR records....
      it will goes like this.. PTR
      Name domain.com (with A to the ip example 1.2.3.4)
      Content 4.3.2.1.in-addr.arpa
      TTL Auto

    i hope someone that had similar problem should fixed with my solution

    2 years later

    I`m using Contabo hosting.
    The support team asked me to add the PTR record from my control panel.
    I have two fields In the Reverse DNS management
    IP ADDRESS ( my server IP address )
    PTR RECORD: mydomain.com ( my real domain )

    But, sometimes I get PTR error from Gmail.

    I must say, my DNS management is with Cloudflare.
    Do I need to add PTR to my Cloudflare DNS records?

      It is recommended to consult the VPS provider and check whether the configuration is effective and correct.