MX TTL Adequacy

What This Check Does

The MX TTL Adequacy check verifies that the Time-to-Live (TTL) value for your MX records is at least 3600 seconds (1 hour). A TTL that is too low causes excessive DNS lookups for your MX records, increasing latency for email delivery and putting unnecessary load on your DNS infrastructure.

DNS Spy reads the TTL value from your MX records and flags any that fall below the 3600-second threshold.

Why It Matters

The MX record TTL controls how long DNS resolvers cache your mail server information. A very low TTL (e.g., 60 or 300 seconds) means every email delivery attempt requires a fresh DNS lookup. This increases email delivery latency, puts more load on your nameservers, and makes your email routing more vulnerable to DNS outages — if your nameservers are briefly unavailable during a low-TTL window, email delivery can fail.

Conversely, an appropriate TTL of 3600 seconds or more ensures MX records are cached effectively, reducing DNS load and providing stability. Mail server changes are infrequent enough that a 1-hour TTL is suitable for most domains.

Good vs. Bad Configuration

Bad Configuration

MX records with a TTL of 300 seconds (5 minutes). Every sending mail server must perform a DNS lookup every 5 minutes, increasing overhead and vulnerability to DNS issues.

Good Configuration

MX records with a TTL of 3600 seconds (1 hour) or higher. DNS resolvers cache your MX records efficiently, reducing lookups and ensuring stable email routing.

How DNS Spy Monitors This

DNS Spy evaluates the TTL of your MX records during each monitoring cycle. If the TTL falls below 3600 seconds, an alert is triggered. DNS Spy also tracks TTL changes over time, helping you verify that configuration updates maintain appropriate values.