mx.no_redundancy
Single MX Target (No Redundancy)
What we check
We count the number of unique MX target IPs after resolving all MX hostnames. A domain with only one mail server IP has no redundancy — if that server is unreachable, all inbound mail is deferred until it recovers.
What this finding means
The domain's MX records resolve to a single IP address. There is no backup mail server. If the primary server goes offline — for maintenance, hardware failure, network issues, or a DDoS attack — sending servers will queue messages and retry, but delivery is delayed until the server is back.
Note: multiple MX records that all resolve to the same IP do not count as redundancy. This check evaluates unique IPs, not the number of MX records.
Why it matters
- Single point of failure. Any outage on the one mail server stops all inbound mail. Sending servers typically retry for 1–5 days before bouncing, but time-sensitive mail (password resets, invoices, two-factor codes) may arrive too late.
- Maintenance windows. Without a backup MX, planned server maintenance causes the same delivery delays as an unplanned outage.
- Common and low-risk. Many small domains legitimately run a single mail server. The penalty is modest because modern sending servers retry reliably, and cloud-hosted mail services provide internal redundancy that is invisible at the MX level.
How to fix
Add a secondary MX pointing to a backup mail server with a higher priority number (lower priority):
example.com. IN MX 10 mail.example.com. example.com. IN MX 20 backup-mx.example.com.Configure the backup server to accept mail for the domain and forward or queue it for the primary.
If using a hosted provider (Google Workspace, Microsoft 365, etc.), check whether the provider's documentation recommends multiple MX records — most large providers already distribute traffic internally and publish multiple MX targets by default.
How it's graded
A single MX target carries a 10-point deduction in the MX category. See Grading Methodology for the full scoring model.
Evidence example
$ dig +short MX example.com
10 mail.example.com.
$ dig +short A mail.example.com
192.0.2.1
Only one MX target IP — no backup mail server