SMTP error code lookup

A bounce message gives you a cryptic code and little else. Search the code below to see what it means, what usually causes it, and what to try next.

How to read a status code

5.1.1
Class — how serious it is
Subject — what area failed
Detail — the exact reason

The first digit tells you what to do next

• 2 — Success. The message was delivered.
• 4 — Temporary. Safe to retry; the server usually will.
• 5 — Permanent. Fix the cause before you resend.

A real bounce often shows two codes together, like 550 5.1.1. The 3-digit code ( 550) is the classic reply; the dotted code ( 5.1.1) is the precise enhanced status. You can paste either — or the whole line — into the search.

Try:

550 5.1.1 mailbox full SPF DKIM blocked TLS

All 139 codes

All 3-digit codes Other Addressing Mailbox Mail system Network Protocol Content Security

2xx

Success & status (2xx / 3xx)

Not errors — greetings, confirmations, and mid-conversation steps. If you see these, things are working.

SMTP error 211: System status or help reply. — read details

211

System status or help reply.

• Common cause: The server is returning diagnostic or status information you asked for.
• Good to know: Not an error — read the text that comes with it.

SMTP error 214: Help reply. — read details

214

Help reply.

• Common cause: A response to the HELP command.
• Good to know: Informational — usually points to the server’s documentation or a FAQ.

SMTP error 220: Service ready. — read details

220

Service ready.

• Common cause: The greeting the server sends when you connect.
• Good to know: Nothing to do — it means the server is up and ready for commands.

... (content continues with similar structure for error codes) ...

No codes match that

Try just the code (like 550 or 4.2.2) or a single keyword. If you pasted a full bounce line, keep only the code part.

Ready when you are

Most rejections come back to sender reputation.

Auth failures, policy blocks, and flood flags (the X.7.x and 5xx codes) are what warmup prevents. Warm up your domain so your mail is trusted before you hit send.