Email hosting

Steve 0 Reputation points
2026-11-08T23:44:37.1833333+00:00

I wish to chat with somebody who can assist me regarding a request for a reverse DNS (PTR) record as I would like to host my smcd.com.au domain on my synology server using their mail plus program, but was told to contact my ISP Telstra, I was informed by my domain host to first contact Microsoft. Can you assist

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  1. Darren Bruce 2,445 Reputation points Independent Advisor
    2026-11-09T00:20:23.13+00:00

    Dear Steve,

    If you're trying to host email on your own Synology MailPlus server and need a reverse DNS (PTR) record, Microsoft is generally not the party that manages PTR records unless the sending IP address belongs to Microsoft.

    If you are hosting email on a Synology MailPlus server, the organization that can create the PTR record is usually:

    • Your ISP (for example, Telstra), if the server is using a static public IP provided by them.
    • Your hosting or cloud provider, if the server is hosted in a datacenter or cloud environment.

    Microsoft can only manage reverse DNS records for IP addresses that belong to Microsoft services such as Exchange Online or Azure. If your mail server is running on your own infrastructure and using a Telstra-assigned IP address, Telstra would generally be the appropriate contact for this request.

    You can refer to this https://www.telstra.com.au/small-business/support/contact-us to contact them

    This link is shared by community members for your convenience. It points to a third-party site that is not managed or verified by Microsoft. We can’t guarantee the quality, safety, or suitability of any content or software found there. Please review carefully and make sure you understand any potential risks before using it.

    I hope it helps, feel free to reach out if you have any other questions.

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  2. AI answer

    2026-11-08T23:45:30.1733333+00:00

    Telstra—not Microsoft or your domain registrar—must create the reverse DNS (PTR) record for the public IP used by your Synology MailPlus server, because Telstra controls that IP address and its reverse-DNS zone.

    Request the PTR record from Telstra

    1. Confirm that your Telstra service has a static public IP address.
      A dynamic or private address is unsuitable for a stable PTR mapping. Telstra documents static IP availability for eligible internet services but does not publish a general self-service PTR process for ordinary static-IP add-ons.^1^
    2. Choose a mail-server hostname, for example: 
         mail.smcd.com.au
    3. At your domain DNS provider, create an A record mapping that hostname to the Telstra public IP: 
         mail.smcd.com.au.  A  <your-static-public-IP>
    4. Ask Telstra to create the matching PTR record: 
         <your-static-public-IP>  PTR  mail.smcd.com.au
      Suggested request:

      Please configure reverse DNS for my static public IP address <IP address>.
      Set its PTR record to mail.smcd.com.au.
      The corresponding A record already resolves mail.smcd.com.au to this IP.
      This is required for an SMTP server running Synology MailPlus.

    5. If this is a Telstra Business, Enterprise, or Wholesale data service, check whether the service appears in CustData. Telstra’s CustData guide says eligible customers can manage reverse-DNS records in the .in-addr.arpa and ip6.arpa zones.^2^ Otherwise, contact Telstra support and ask for the request to be routed to the team responsible for static-IP reverse DNS. Microsoft cannot make this change on a Telstra-owned address.

    Configure the other mail DNS records

    The PTR record is separate from the DNS zone for your domain. Your domain DNS host should still hold:

    • An MX record directing incoming email to mail.smcd.com.au.
    • An A record directing mail.smcd.com.au to the public IP.
    • One SPF TXT record authorizing that IP to send mail.
    • DKIM records generated/configured by MailPlus.
    • A DMARC record aligned with the domain used in the From address.

    Microsoft notes that reverse DNS can be used as fallback authentication, but it is not a substitute for correctly configured SPF, DKIM, and DMARC.^3^ Microsoft 365 might reject senders whose reverse-DNS lookup fails.^4^

    Also configure MailPlus so its SMTP HELO/EHLO hostname is the same hostname used by the PTR record—such as mail.smcd.com.au.

    If Telstra cannot provide PTR service

    Do not create a PTR record in your ordinary domain DNS panel; that does not control reverse DNS for Telstra’s IP. The practical alternatives are:

    • Use an SMTP relay provider that supplies suitable reverse DNS.
    • Host outbound mail with Microsoft 365/Exchange Online or another mail provider.
    • Move to a business internet service that supports static IP and reverse DNS.

    If you instead move all email hosting to Microsoft 365, its domain setup uses MX, SPF, Autodiscover, DKIM, and related records; Microsoft operates the reverse DNS for its own outbound servers.^5^

    References

    1. What Is an IP Address (Dynamic and Static)? | Telstra
    2. CUSTDATA USER GUIDE - Telstra
    3. Security Operations guide for email authentication in Microsoft 365
    4. External senders - Troubleshoot email sent to Microsoft 365
    5. External Domain Name System records for Microsoft 365
    AI-generated content may be incorrect. Read our transparency notes for more information.

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