Bad destination system address — domain does not exist or has no MX record
Production Risk
Medium — invalid domains inflate bounce rates and harm sender reputation.
The destination domain either does not exist in DNS or has no valid MX (Mail Exchanger) records. The message cannot be delivered because there is no mail server to receive it.
- 1The domain in the recipient address is misspelled or does not exist.
- 2The domain has expired and its DNS records have been removed.
- 3The domain exists but has no MX records configured.
Sending mail to an address whose domain has no resolvable MX record.
RCPT TO:<user@nonexistentdomain.example> # Server returns: 550 5.1.2 Bad destination mailbox address
expected output
550 5.1.2 ...
Fix
Validate domain MX records before sending
WHEN Before adding an address to your list or on bounce
# Check MX records for a domain
dig MX example.com +short
# Or in Node.js:
dns.resolveMx('example.com', (err, addresses) => { ... });Why this works
DNS MX lookup at list signup time prevents invalid domains from entering your database.
✕ Retry delivery to a domain with no MX
Without an MX record the domain cannot receive email. This is a permanent failure.
RFC 3463 — Enhanced Mail System Status Codes
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