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How to Configure Helo Domain (FQDN) and PTR record to pass FCrDNS check

In Send Connector of EA SMTP Server, configuring correct Helo Domain (FQDN) is necessary to ensure that outgoing emails pass the Forward Confirmed reverse DNS (FCrDNS) check. By default, EA SMTP Server uses current machine’s hostname or domain as the Helo Domain (FQDN), it cannot pass the FCrDNS check unless properly configured.

What is FCrDNS

FCrDNS (Forward Confirmed reverse DNS) is a method used to verify that the IP address of an email sender matches the domain name specified in the reverse DNS record. This helps prevent email spoofing and ensures that outgoing emails are properly authenticated.

  1. PTR (reverse DNS): Your sending public IP resolves to a hostname.
  2. A‑record (forward DNS): That same hostname must resolve back to your original sending IP.

If this loop does not match, many anti‑spam systems reject mail with 550 5.7.25 error.

For example, if your server’s IP address is 192.0.2.1 and the reverse DNS record for this IP points to mail.example.com, then the Helo Domain (FQDN) should be set to mail.example.com, and mail.example.com should resolve back to 192.0.2.1 in the forward DNS lookup.

  • PTR record must be configured with your IP provider.
  • A record must be configured with your domain provider.

How to Verify FCrDNS

You can use the following commands to verify FCrDNS:

nslookup -type=PTR 192.0.2.1
# This should return mail.example.com
nslookup -type=A mail.example.com
# This should return 192.0.2.1, then you can confirm that the FCrDNS check passes.
# If the above checks are successful, input the same hostname in the Helo Domain (FQDN) field of your EA SMTP Server send connector.

To configure the Helo Domain (FQDN):

  1. Open the EA SMTP Server management console.
  2. Navigate to the Send Connector section.
  3. Select the send connector you want to configure and click Edit.
  4. In the Helo Domain (FQDN) field, enter a valid domain name that matches the reverse DNS record of your server’s IP address.
  5. Save the changes, no restart is required for the new Helo Domain (FQDN) to take effect.

Test online

You can use the following online tools to verify FCrDNS for your domain.

https://appmaildev.com/en/dkim

Get a test email address from above website to send a test email and verify the Helo Domain (FQDN) configuration. It also verifies SPF/DKIM/DMARC records.

Free for non-commercial use

EA SMTP Server is free for non-commercial use. You can request a trial license every 60 days, and each trial license is valid for 90 days. When your trial license is close to expiring, you can apply for a new one to continue using the server for non-commercial projects.

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Support@EmailArchitect.NET

Remarks

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