smtp-error-codes/
138 pages · Updated 2026-10-27
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- SMTP Error X.7.30 - REQUIRETLS support required | Warmup Inbox
- SMTP Error X.7.29 - ARC validation failure | Warmup Inbox
- SMTP Error X.7.27 - Sender address has null MX | Warmup Inbox
- SMTP Error X.7.28 - Mail flood detected | Warmup Inbox
- SMTP Error X.7.26 - Multiple authentication checks failed | Warmup Inbox
- SMTP Error X.7.24 - SPF validation error | Warmup Inbox
- SMTP Error X.7.25 - Reverse DNS validation failed | Warmup Inbox
- SMTP Error X.7.23 - SPF validation failed | Warmup Inbox
- SMTP Error X.7.22 - No valid author-matched DKIM signature | Warmup Inbox
- SMTP Error X.7.21 - No acceptable DKIM signature found | Warmup Inbox
- SMTP Error X.7.20 - No passing DKIM signature found | Warmup Inbox
- SMTP Error X.7.19 - RRVS test cannot be completed | Warmup Inbox
- SMTP Error X.7.18 - Domain owner has changed | Warmup Inbox
- SMTP Error X.7.17 - Mailbox owner has changed | Warmup Inbox
- SMTP Error X.7.16 - Message too big for specified priority | Warmup Inbox
- SMTP Error X.7.15 - Priority level too low | Warmup Inbox
- SMTP Error X.7.14 - Trust relationship required | Warmup Inbox
- SMTP Error X.7.13 - User account disabled | Warmup Inbox
- SMTP Error X.7.12 - Password transition needed | Warmup Inbox
- SMTP Error X.7.11 - Encryption required for authentication mechanism | Warmup Inbox
- SMTP Error X.7.10 - Encryption needed | Warmup Inbox
- SMTP Error X.7.9 - Authentication mechanism too weak | Warmup Inbox
- SMTP Error X.7.7 - Message integrity failure | Warmup Inbox
- SMTP Error X.7.8 - Authentication credentials invalid | Warmup Inbox
- SMTP Error X.7.6 - Cryptographic algorithm not supported | Warmup Inbox
- SMTP Error X.7.5 - Cryptographic failure | Warmup Inbox
- SMTP Error X.7.1 - Delivery not authorized | Warmup Inbox
- SMTP Error X.7.4 - Security features not supported | Warmup Inbox
- SMTP Error X.7.3 - Security conversion required but impossible | Warmup Inbox
- SMTP Error X.7.2 - Mailing list expansion prohibited | Warmup Inbox
- SMTP Error X.6.10 - Deprecated | Warmup Inbox
- SMTP Error X.7.0 - Other or undefined security status | Warmup Inbox
- SMTP Error X.6.8 - UTF-8 reply required but not permitted | Warmup Inbox
- SMTP Error X.6.9 - UTF-8 header cannot be transferred | Warmup Inbox
- SMTP Error X.6.7 - Non-ASCII addresses not permitted | Warmup Inbox
- SMTP Error X.6.6 - Message content not available | Warmup Inbox
- SMTP Error X.6.4 - Conversion with loss performed | Warmup Inbox
- SMTP Error X.6.5 - Conversion failed | Warmup Inbox
- SMTP Error X.6.2 - Conversion required and prohibited | Warmup Inbox
- SMTP Error X.6.3 - Conversion required but unsupported | Warmup Inbox
- SMTP Error X.6.1 - Media not supported | Warmup Inbox
- SMTP Error X.6.0 - Other or undefined media error | Warmup Inbox
- SMTP Error X.5.4 - Invalid command arguments | Warmup Inbox
- SMTP Error X.5.3 - Too many recipients | Warmup Inbox
- SMTP Error X.5.6 - Authentication exchange line too long | Warmup Inbox
- SMTP Error X.5.5 - Wrong protocol version | Warmup Inbox
- SMTP Error X.5.2 - Syntax error | Warmup Inbox
- SMTP Error X.5.1 - Invalid command | Warmup Inbox
- SMTP Error X.5.0 - Other or undefined protocol status | Warmup Inbox
- SMTP Error X.4.7 - Delivery time expired | Warmup Inbox
- SMTP Error X.4.6 - Routing loop detected | Warmup Inbox
- SMTP Error X.4.5 - Mail system congestion | Warmup Inbox
- SMTP Error X.4.4 - Unable to route | Warmup Inbox
- SMTP Error X.4.3 - Directory server failure | Warmup Inbox
- SMTP Error X.4.2 - Bad connection | Warmup Inbox
- SMTP Error X.4.1 - No answer from host | Warmup Inbox
- SMTP Error X.4.0 - Other or undefined network / routing status | Warmup Inbox
- SMTP Error X.3.6 - Requested priority changed | Warmup Inbox
- SMTP Error X.3.4 - Message too big for system | Warmup Inbox
- SMTP Error X.3.3 - System not capable of selected features | Warmup Inbox
- SMTP Error X.3.1 - Mail system full | Warmup Inbox
- SMTP Error X.3.2 - System not accepting network messages | Warmup Inbox
- SMTP Error X.3.0 - Other or undefined mail system status | Warmup Inbox
- SMTP Error X.2.4 - Mailing list expansion problem | Warmup Inbox
- SMTP Error X.2.2 - Mailbox full | Warmup Inbox
- SMTP Error X.2.1 - Mailbox disabled | Warmup Inbox
- SMTP Error X.2.0 - Other or undefined mailbox status | Warmup Inbox
- SMTP Error X.1.10 - Recipient address has null MX | Warmup Inbox
- SMTP Error X.1.9 - Relayed to non-compliant mailer | Warmup Inbox
- SMTP Error X.1.8 - Bad sender system address | Warmup Inbox
- SMTP Error X.1.7 - Bad sender mailbox address syntax | Warmup Inbox
- SMTP Error X.1.6 - Destination mailbox moved, no forwarding address | Warmup Inbox
- SMTP Error X.1.5 - Destination address valid | Warmup Inbox
- SMTP Error X.1.3 - Bad destination mailbox address syntax | Warmup Inbox
- SMTP Error X.1.4 - Destination mailbox address ambiguous | Warmup Inbox
- SMTP Error X.1.2 - Bad destination system address | Warmup Inbox
- SMTP Error X.1.1 - Bad destination mailbox address | Warmup Inbox
- SMTP Error 554 - Transaction failed. | Warmup Inbox
- SMTP Error X.1.0 - Other address status | Warmup Inbox
- SMTP Error X.0.0 - Other or undefined status | Warmup Inbox
- SMTP Error 552 - Storage allocation exceeded / message too large. | Warmup Inbox
- SMTP Error 553 - Mailbox name not allowed / invalid address. | Warmup Inbox
- SMTP Error 551 - User not local; relay denied. | Warmup Inbox
- SMTP Error 550 - Mailbox unavailable / address rejected. | Warmup Inbox
- SMTP Error 541 - Recipient address rejected the message. | Warmup Inbox
- SMTP Error 503 - Bad sequence of commands. | Warmup Inbox
- SMTP Error 535 - Authentication failed. | Warmup Inbox
- SMTP Error 530 - Authentication required. | Warmup Inbox
- SMTP Error 504 - Command parameter not implemented. | Warmup Inbox
- SMTP Error 502 - Command not implemented. | Warmup Inbox
- SMTP Error 501 - Syntax error in parameters or arguments. | Warmup Inbox
- SMTP Error 555 - MAIL FROM / RCPT TO parameters not recognized or not implemented. | Warmup Inbox
- SMTP Error 556 - Domain does not accept mail (null MX). | Warmup Inbox
- SMTP Error 500 - Syntax error — command unrecognized. | Warmup Inbox
- SMTP Error 547 - Delivery time expired — a garbled form of 5.4.7, not a real code. | Warmup Inbox
- SMTP Error 543 - Not a real code — a mislabel of enhanced status 5.4.4 "unable to route". | Warmup Inbox
- SMTP Error 546 - Not a real code — a label for a mail loop (554 5.4.6). | Warmup Inbox
- SMTP Error 542 - Not a real SMTP code — a blog "bad connection" label. | Warmup Inbox
- SMTP Error 538 - Encryption required for the requested authentication mechanism. | Warmup Inbox
- SMTP Error 534 - Authentication mechanism too weak. | Warmup Inbox
- SMTP Error 531 - Not a real code — usually mail-system-full (4.3.1 / 552) or an auth failure. | Warmup Inbox
- SMTP Error 540 - Not a real code — usually 5.4.0, or a provider literal rejection. | Warmup Inbox
- SMTP Error 523 - Message length exceeds administrative limit — enhanced 5.2.3 flattened. | Warmup Inbox
- SMTP Error 521 - Host does not accept mail. | Warmup Inbox
- SMTP Error 515 - Invalid recipient address — not a real RFC code. | Warmup Inbox
- SMTP Error 512 - Domain not found — a vendor label for enhanced status 5.1.2. | Warmup Inbox
- SMTP Error 510 - Invalid recipient address — a vendor label, not a real code. | Warmup Inbox
- SMTP Error 533 - Non-standard label, usually a misread of 5.3.3. | Warmup Inbox
- SMTP Error 522 - Mailbox full — a non-standard label for 552 / 5.2.2. | Warmup Inbox
- SMTP Error 513 - Non-standard label: bad address syntax, or a relay/auth failure. | Warmup Inbox
- SMTP Error 454 - Temporary authentication failure, or TLS not available. | Warmup Inbox
- SMTP Error 517 - Non-standard label: bad sender attribute, or a policy block. | Warmup Inbox
- SMTP Error 511 - Bad destination mailbox address — a misread of 5.1.1, not a real code. | Warmup Inbox
- SMTP Error 455 - Server unable to accommodate parameters. | Warmup Inbox
- SMTP Error 432 - Recipient incoming mail queue stopped (Exchange). | Warmup Inbox
- SMTP Error 431 - Server out of memory or disk (temporary). | Warmup Inbox
- SMTP Error 452 - Insufficient system storage or too many recipients. | Warmup Inbox
- SMTP Error 451 - Requested action aborted — local error in processing. | Warmup Inbox
- SMTP Error 450 - Mailbox unavailable (temporary). | Warmup Inbox
- SMTP Error 421 - Service not available, closing channel. | Warmup Inbox
- SMTP Error 446 - Maximum hop count exceeded — a label for a mail loop, not a real code. | Warmup Inbox
- SMTP Error 442 - Connection dropped during transmission — a tool label, not a real code. | Warmup Inbox
- SMTP Error 441 - No answer from host — a misread of 4.4.1, or an AuthSMTP quota code. | Warmup Inbox
- SMTP Error 422 - Mailbox full — a misread of enhanced status 4.2.2, not a real code. | Warmup Inbox
- SMTP Error 471 - Local filter or Exchange block — not a valid SMTP code. | Warmup Inbox
- SMTP Error 458 - Unable to queue messages for node — the ETRN failure reply. | Warmup Inbox
- SMTP Error 449 - Exchange routing error — non-standard, legacy Exchange only. | Warmup Inbox
- SMTP Error 447 - Delivery time expired — a misread of 4.4.7, not a real code. | Warmup Inbox
- SMTP Error 420 - TCP read/write timeout — non-standard, mostly GroupWise. | Warmup Inbox
- SMTP Error 252 - Cannot verify recipient, will attempt delivery. | Warmup Inbox
- SMTP Error 251 - User not local; will forward. | Warmup Inbox
- SMTP Error 221 - Service closing transmission channel. | Warmup Inbox
- SMTP Error 250 - Requested action completed. | Warmup Inbox
- SMTP Error 235 - Authentication successful. | Warmup Inbox
- SMTP Error 220 - Service ready. | Warmup Inbox
- SMTP Error 214 - Help reply. | Warmup Inbox
- SMTP Error 211 - System status or help reply. | Warmup Inbox
- SMTP Error Code Lookup — Meanings, Causes & Fixes | Warmup Inbox