TL;DR
Disabled or provider-specific receiving-rate condition: no unchanged retry; inspect the reply before suppression.
What this code means
X.2.1 means mailbox disabled and not accepting messages, but the catalog has no IANA class confirmation for that pattern. Gmail’s exact 5.2.1 examples cover disabled or inactive accounts and a different ReceivingRatePerm condition.
Provider examples
smtp;550 5.2.1 The email account that you tried to reach is disabled. Learn more at https://support.google.com/mail/?p=DisabledUser - gsmtp550 5.2.1 The email account that you tried to reach is inactive. Learn more at https://support.google.com/mail/?p=DisabledUser - gsmtpsmtp;550 5.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered. For more information, please visit https://support.google.com/mail/?p=ReceivingRatePerm - gsmtp<ben@enhance.com>: host aspmx.l.google.com[124.205.72.72] said: 550-5.2.1 The email account that you tried to reach is inactive. Learn more at 550 5.2.1 https://support.google.com/mail/?p=DisabledUser 7-20020a508e47000000b0054864c701a3si879110edx.134 - gsmtp (in reply to RCPT TO command)Technical meaning
The digits alone do not prove a nonexistent address. The reply text distinguishes a disabled account from Gmail’s receiving-rate response.
Delivery status
Class 5 is permanent for this attempt; it does not certify that the account can never be re-enabled.
- Class
- Permanent failure
- Retry
- Do not retry unchanged
- Suppression
- Check the full context
Retry decision
Stop unchanged retries. Consider a new attempt only after independent confirmation that the account is active again or the stated provider condition changed.
Suppression decision
Treat a confirmed disabled account as an address-review signal, not automatic irreversible removal. Revalidate because the account may return; do not use a rate response as proof of closure.
Common causes
- The mailbox is disabled, or Gmail reports a permanent receiving-rate condition in the full reply.
Diagnostic steps
- Preserve the full response and recent delivery history; distinguish disabled-account text from receiving-rate text before acting.
Actions by owner
Sender
- Stop unchanged sends and seek confirmation through another channel before reattempting.
Recipient
- If the account was disabled unexpectedly, contact the provider or domain administrator.
Recipient administrator
- Confirm whether an account was intentionally disabled and re-enable it only when appropriate.
Sources
These sources define what this enhanced status code means, mainly through the IANA registry and related RFCs. When provider examples appear on the page, they come from that provider's published documentation. Follow the links to read the original wording in context.
- RFC 3463 — Enhanced Mail System Status Codes — Defines the class/subject/detail model for enhanced status codes.
- RFC 5248 — A Registry for SMTP Enhanced Mail System Status Codes — Creates and governs the IANA enhanced status code registry.
- Fix bounced or rejected emails — Gmail Help article covering disabled-account and bulk-sender rate-limit responses.
- smtp-codes (community corpus) — Community-maintained reference of provider SMTP responses, pinned locally as evidence.
- Fix bounced or rejected emails — receiving rate limit (permanent) — Gmail Help article for the permanent recipient receiving-rate condition (550 5.2.1).
- email-bounce-parser (test fixture corpus) — Open-source bounce-parsing library whose test fixtures are pinned locally as evidence.
Last verified:
