SMTP-CERT-INVALID
Mail server certificate does not verify
What it means
Self-signed or expired certificates prevent verified TLS. MTA-STS enforce mode would cause delivery failures.
How to fix it
- 1Install a certificate from a public CA with the full chain.
Re-check after the change
DNS changes can take up to the record's TTL to be seen; use Re-run on the result page to bypass our 10-minute cache.