Email Network Security Blog

Email Filtering Service: Using FQDN Versus an IP Address as Destination Relay

Email filtering service providers like Sentinare Messaging Solutions accept mail via MX records, filter out spam and viruses, and then, using SMTP, relay the email to the “destination relay”, which is your mail server at your customer site. Typically you can configure the filtering service provider to relay to either a FQDN (Fully Qualified Domain Name) or to an IP address.

There are implications with both. With a FQDN, you can change the IP and update the DNS without having to notify the email filtering service provider of the new IP address. The downside of FQDN is if you have DNS problems and the provider cannot look up the FQDN.

The upside of an IP is that it doesn’t rely on DNS. The downside is that you must notify your provider of any IP changes.

We at Sentinare Messaging Solutions prefer FQDN. You should have enough redundancy in your DNS to prevent any problems with DNS and this will make your life easier. By using FQDNs for your mail destination addresses, you have more control and flexibility. If the IP address of your mail server changes, you can control the destination server change and don’t have to notify your email filtering service provider of the IP address change.