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Error code wiki · 111 codes

Microsoft SMTP error codes

Microsoft runs Outlook.com, the consumer service behind outlook.com, hotmail.com, live.com and msn.com addresses, and Exchange Online, which receives mail for business domains hosted on Microsoft 365.

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Permanent failures (5xx)

97 codes

The receiving server refused the message for good. Your server will not try again, and the message comes back to you as a bounce.

  1. 5.1.90Daily recipient limit reached.The sending mailbox has reached the Exchange Online recipient rate limit for a 24-hour period and cannot send to more recipients for now.Permanent
  2. 5.2.2Submission quota exceeded.The sender went over the Exchange Online recipient or message rate limit, so Microsoft 365 refused to accept more mail from the account.Permanent
  3. 5.2.121Too many messages to one recipient this hour.The sender has gone over the number of messages Exchange Online lets one sender deliver to the same recipient within an hour.Permanent
  4. 5.2.122Recipient has received too many messages this hour.The Microsoft 365 recipient has hit the hourly limit on messages it can receive from all senders combined, so new mail is refused for now.Permanent
  5. 5.3.190On-premises journaling to Microsoft 365 not enabled.An on-premises journal rule sends journal reports to Microsoft 365, but the organization does not have Journaling Archive turned on.Permanent
  6. 5.4.1Server does not accept mail for this domain.The server that answered does not accept mail for the recipient's domain, which usually points to a wrong MX record or server setting.Permanent
  7. 5.4.8Destination MX not covered by its MTA-STS policy.Exchange Online did not deliver because the receiving MX host is missing from the destination domain's MTA-STS policy.Permanent
  8. 5.4.300Message expired and the report could not be returned.The message was not delivered in time because the destination did not respond or an error occurred, and the report could not reach the sender.Permanent
  9. 5.7.1Unable to relay.The receiving system refused to pass the message on because it is not the final destination for the recipient domain.Permanent
  10. 5.7.1IP listed on both a connector and the IP Allow list.An outside server's IP is set on both an inbound connector and the IP Allow list, which hides the real blocklist that refused it.Permanent
  11. 5.7.1Sending IP on the Microsoft 365 blocklist.Microsoft 365 refused the message because the sending IP address is on its own blocklist, named Blocklist 1 in the bounce.Permanent
  12. 5.7.5Destination certificate fails MTA-STS.Exchange Online stopped delivery because the receiving server's TLS certificate does not satisfy the destination domain's MTA-STS policy.Permanent
  13. 5.7.12Recipient accepts mail only from its organization.The address you wrote to takes mail only from inside its own organization, so outside senders are refused until that organization's admin changes the setting.Permanent
  14. 5.7.25IPv6 sender without reverse DNS.Microsoft 365 refused mail from an IPv6 address that has no reverse DNS (PTR) record; the same rule also appears as 450 4.7.25.Permanent
  15. 5.7.129No permission to send to the recipient.You were refused permission to send to the recipient; Microsoft documents this for mailboxes whose on-premises account was disabled.Permanent
  16. 5.7.232Trial tenant reached its external recipient limit.A Microsoft 365 trial tenant sent to more external recipients in 24 hours than its tenant external recipient rate limit allows.Permanent
  17. 5.7.233Tenant reached its external recipient limit.The Microsoft 365 tenant sent to more external recipients in 24 hours than its tenant external recipient rate limit allows.Permanent
  18. 5.7.321Destination server does not offer TLS (DANE).Exchange Online needed TLS for this domain under DANE, but the receiving server did not answer STARTTLS or the handshake failed.Permanent
  19. 5.7.322Destination certificate expired (DANE).The receiving server presented an expired certificate on a domain protected by DANE, so Exchange Online did not send.Permanent
  20. 5.7.323Certificate does not match the TLSA record (DANE).The destination's DNSSEC-signed TLSA records do not match the certificate its server presented, so Exchange Online treated delivery as unsafe.Permanent
  21. 5.7.324Destination DNSSEC does not validate.The destination domain signals DNSSEC protection, but Exchange Online could not validate its records, so delivery stopped.Permanent
  22. 5.7.325Certificate name does not match the MX host (DANE).The receiving server's certificate does not name the destination domain or its MX host, so Exchange Online would not deliver under DANE.Permanent
  23. 5.7.501Sending account banned for spam abuse.Microsoft 365 banned the sending account after detecting spam from it; Microsoft support has to restore its ability to send.Permanent
  24. 5.7.502–503Banned sender account.Microsoft 365 banned the sending account for detected spam activity; codes 5.7.502 and 5.7.503 carry the same description.Permanent
  25. 5.7.504Recipient address not valid.Microsoft 365 rejected the recipient address as not valid; check the address and try again.Permanent
  26. 5.7.505Banned recipient.Microsoft 365 refused the message because the recipient you are writing to is not valid there.Permanent
  27. 5.7.506Bad HELO name.Your server greeted Microsoft 365 with the name of the server it was connecting to, instead of its own fully qualified domain name.Permanent
  28. 5.7.507Sending IP blocked by the recipient organization.The recipient's organization has blocked the IP address you send from; only the recipient can lift the block.Permanent
  29. 5.7.508IPv6 range sending too fast.The sender's IPv6 range sent too many messages in too short a time, so Microsoft 365 refused further mail from it.Permanent
  30. 5.7.509DMARC failure with a reject policy.The domain in the From address failed DMARC and publishes p=reject, so Microsoft 365 rejected the message as the domain asked.Permanent
  31. 5.7.510Recipient domain does not accept IPv6 mail.You sent over IPv6 to a Microsoft 365 domain whose tenant has not opted in to receiving anonymous mail over IPv6.Permanent
  32. 5.7.512Message has no valid From address.Microsoft 365 rejected the message because its From header does not contain a valid email address, as RFC 5322 section 3.6.2 requires.Permanent
  33. 5.7.513Sending IP on the recipient's custom block list.The recipient domain added your sending IP address to its own custom block list, so its Microsoft 365 tenant refuses your mail.Permanent
  34. 5.7.520Automatic external forwarding blocked.Exchange Online stopped an automatically forwarded message because the organization's outbound spam policy blocks forwarding to external addresses.Permanent
  35. 5.7.800Sending domain banned.Microsoft banned the domain used in this message's EHLO, envelope sender or From address because of detected spam activity.Permanent
  36. 530 5.7.1Client was not authenticated.The receiving server requires authentication before it accepts a message, and the sending system did not authenticate.Permanent
  37. 535 5.7.142HVE: OAuth token about to expire.The OAuth access token an application used to authenticate to HVE was close to expiring, so Exchange Online rejected it.Permanent
  38. 535 5.7.143HVE: OAuth token expired.The application tried to authenticate to HVE with an OAuth access token that had already expired.Permanent
  39. 535 5.7.144HVE: app lacks the right API permissions.The OAuth token came from an app registration whose API permissions do not allow it to use HVE, so authentication failed.Permanent
  40. 550Domain record allows no senders (Sender ID).Outlook.com refused the mail because the sending domain publishes a record saying no server may send for it, such as v=spf1 -all.Permanent
  41. 550 [DY-001]Outlook.com refuses dynamic IP addresses.Outlook.com rejected the mail because the sending IP is dynamic address space, which it generally does not accept mail from.Permanent
  42. 550 [DY-002]Outlook.com block for a likely compromised sender.Outlook.com rejected the mail because the sending server or computer appears to be compromised or infected.Permanent
  43. 550 [OU-001]Outlook.com block linked to Spamhaus.Outlook.com rejected the mail for policy reasons and points you to Spamhaus for details of the block and for removal.Permanent
  44. 550 [OU-002]Outlook.com rejection for content or reputation.Outlook.com rejected the mail for policy reasons that may relate to spam-like content or the reputation of the sending IP or domain.Permanent
  45. 550 [SC-001]Outlook.com policy block for content or reputation.Outlook.com rejected the mail for policy reasons tied to spam-like content or to the reputation of the sending IP or domain.Permanent
  46. 550 [SC-002]Outlook.com block for namespace mining.Outlook.com blocked the sending IP because it behaved like a namespace miner, checking whether addresses exist without sending mail.Permanent
  47. 550 [SC-003]Outlook.com block for an open proxy or relay.Outlook.com rejected the mail because the sending IP appears to be an open proxy or open relay.Permanent
  48. 550 [SC-004]Outlook.com block after complaints.Outlook.com placed a block on the sending IP because it received complaints about mail coming from it.Permanent
  49. 550 5.0.350Generic error from the recipient's system.Exchange Online wraps an unspecific rejection from the recipient's mail system in 5.0.350; the real reason is in the original reply quoted in the report.Permanent
  50. 550 5.0.350Rich Text attachment makes a header too long.A message in Outlook's Rich Text format carried an attachment whose data ended up in a header line too long for the receiving server.Permanent
  51. 550 5.0.350 [AS345]Attachment with too many embedded files.The message was rejected because an attachment contains 20 or more embedded files, which is treated as a policy violation.Permanent
  52. 550 5.1.0Sender denied.The destination server refused messages from you or for this recipient, often because the sender is blocked or a cached address is stale.Permanent
  53. 550 5.1.1Recipient address not found.The address does not exist in the destination system, is mistyped, or is cached in Outlook with details that are no longer valid.Permanent
  54. 550 5.1.8Account blocked for sending spam.Microsoft 365 has blocked this user from sending because the account sent spam or exceeded its sending limits, usually after a compromise.Permanent
  55. 550 5.1.10Recipient not found by SMTP address lookup.The recipient's domain is served by Exchange Online, but no recipient there has the address you sent to.Permanent
  56. 550 5.1.20Several From addresses but no Sender.The message lists more than one address in its From header and none in its Sender header, which RFC 5322 does not allow.Permanent
  57. 550 5.1.241Recipient is a send-only HVE account.The message was addressed to an HVE account, which can only send and has no mailbox to receive mail.Permanent
  58. 550 5.2.0External contact has no valid primary address.Exchange Online could not deliver to an external contact because its primary SMTP address is missing from its proxy addresses or invalid.Permanent
  59. 550 5.2.240HVE account not set up correctly.The account used to submit the message is not configured correctly for High Volume Email, so the submission was rejected.Permanent
  60. 550 5.2.241HVE account has no billing policy.The HVE account lacks a valid billing configuration, so Exchange Online will not accept messages from it.Permanent
  61. 550 5.4.1Recipient rejected by Directory-Based Edge Blocking.Microsoft 365 rejected the message at its edge because the recipient address does not exist in the destination tenant.Permanent
  62. 550 5.5.0Outlook.com or Hotmail address not found.Microsoft found no mailbox with this address at hotmail.com or outlook.com; it works like 5.1.10 for consumer addresses.Permanent
  63. 550 5.6.0Moderation fails without an expiry policy tag.A message to a moderated group failed because the approval agent needs a retention tag that the organization has not created.Permanent
  64. 550 5.6.11Message contains bare line feeds.The message contains bare line feeds, and the destination server does not support the SMTP BDAT command needed to accept them.Permanent
  65. 550 5.6.240HVE: MIME header not allowed.The message submitted through HVE contains a MIME header that the service does not permit.Permanent
  66. 550 5.6.241HVE: From header missing or invalid.The message submitted through HVE has no valid From header, or the header is formatted incorrectly.Permanent
  67. 550 5.7.1Not authorized to send to this recipient.You do not have permission to send to this recipient, typically a group restricted to certain senders or a recipient protected by a mail flow rule.Permanent
  68. 550 5.7.1Public folder does not accept external mail.An external sender wrote to a mail-enabled public folder in Microsoft 365, which by default accepts mail only from authenticated senders.Permanent
  69. 550 5.7.13No permission to post to the public folder.Delivery to a mail-enabled public folder failed because the permission the sender falls under does not allow creating items in it.Permanent
  70. 550 5.7.23SPF violation on outgoing mail.The destination checked SPF on mail sent from your Microsoft 365 organization and rejected it, which points to a problem in your SPF setup.Permanent
  71. 550 5.7.57SMTP client submission without authentication.A device or application tried to send through smtp.office365.com without authenticating as a user with an Exchange Online mailbox.Permanent
  72. 550 5.7.64Relay not attributed to your tenant.Microsoft 365 could not match your on-premises server to an inbound connector, so it refused to relay its mail.Permanent
  73. 550 5.7.124Sender not in the group's allowed senders.The distribution group accepts mail only from listed senders, and you are not on its list, directly or through a group.Permanent
  74. 550 5.7.128Transport rules redirected the message too many times.Transport rules in one or more organizations kept redirecting the message, and Exchange Online stopped it at the redirection limit.Permanent
  75. 550 5.7.133Group rejects mail from outside the organization.The recipient is a distribution group set to reject messages from senders outside its organization.Permanent
  76. 550 5.7.134Mailbox rejects mail from outside the organization.The recipient mailbox is set to accept only authenticated senders, so mail from outside its organization is rejected.Permanent
  77. 550 5.7.135Public folder rejects mail from outside.The recipient is a mail-enabled public folder set to reject messages from senders outside its organization.Permanent
  78. 550 5.7.136Mail user rejects mail from outside.The recipient is a mail user set to reject messages from senders outside its organization.Permanent
  79. 550 5.7.193Microsoft 365 group does not accept external mail.An outside sender wrote to a Microsoft 365 group that does not allow external senders, or the sender is not a member.Permanent
  80. 550 5.7.236onmicrosoft.com domain reached its external limit.The tenant sent to more than 100 external recipients in 24 hours from its onmicrosoft.com domain, which Microsoft intends for testing only.Permanent
  81. 550 5.7.240HVE: application not allowed.The application used to send is not authorized for HVE accounts, so Exchange Online rejected the message.Permanent
  82. 550 5.7.241–243HVE: tenant cannot use High Volume Email.The tenant is not eligible for HVE: 5.7.241 for a trial tenant, 5.7.242 for an inactive tenant, and 5.7.243 for a blocked tenant.Permanent
  83. 550 5.7.244–245HVE: external recipients not supported.HVE accounts can send only to recipients inside the organization, so messages to outside addresses are rejected.Permanent
  84. 550 5.7.246HVE: external recipients removed after expansion.External recipients that came from expanding a distribution list were dropped, because HVE does not support external recipients.Permanent
  85. 550 5.7.367Forwarded mail rejected by the next hop.A message Microsoft 365 forwarded or relayed was refused by the next server, often a third-party gateway, because it left from Microsoft's relay pool.Permanent
  86. 550 5.7.511Banned sending IP: request removal by email.Microsoft 365 banned the IP you send from and wants to investigate before lifting it; the delist portal cannot remove this block.Permanent
  87. 550 5.7.515Outlook.com high-volume sender authentication.Outlook.com rejected mail from a domain that sends over 5,000 messages a day to it, because the mail did not pass SPF, DKIM and DMARC.Permanent
  88. 550 5.7.606–649Banned sending IP: use the delist portal.Microsoft 365 put your sending IP on its blocked senders list; you can request removal yourself at sender.office.com.Permanent
  89. 550 5.7.703Recipient blocked by your Tenant Allow/Block List.Someone in your organization sent to an address or domain that your own Tenant Allow/Block List blocks, so the whole message was stopped.Permanent
  90. 550 5.7.705Tenant blocked for sending spam.Exchange Online blocked outgoing mail from your whole tenant because too much of its traffic was spam or bulk mail.Permanent
  91. 550 5.7.708Traffic not accepted from this IP.Microsoft 365 refused mail from the sending IP because of its low reputation; Microsoft says new tenants such as trials are most affected.Permanent
  92. 550 5.7.750Sending from unregistered domains.The tenant sent a suspicious volume of mail from domains that are not added and verified in Microsoft 365, so Exchange Online blocked it.Permanent
  93. 552 5.3.4Message headers too large.Exchange Online rejected the message because its headers add up to more than 256 KB, the limit for all header fields together.Permanent
  94. 554 5.2.0Clutter folder missing in the recipient mailbox.Delivery to one Exchange Online mailbox fails because Clutter is turned on for it but its Clutter folder is missing.Permanent
  95. 554 5.2.2Mail-enabled public folder is full.Delivery to a mail-enabled public folder failed because the folder, the organization default, or its public folder mailbox reached its quota.Permanent
  96. 554 5.4.14Hop count exceeded, possible mail loop.The message passed between servers so many times that Exchange stopped it as a likely mail loop; 5.4.6 is the on-premises form.Permanent
  97. 554 5.6.0Attachment scan timed out under a transport rule.A Word or Excel attachment could not be scanned in time by a transport rule set to defer on failure, so the message was returned.Permanent

Temporary failures (4xx)

14 codes

The receiving server cannot take the message now. Your server keeps it and retries, and only bounces it if the retries run out.

  1. 4.3.2Mailbox folder holds too many items.Exchange Online cannot deliver to this mailbox because one of its folders has reached the limit of one million items.Temporary
  2. 4.4.7Message expired in the queue.Exchange Online kept retrying a message for a day, the receiving server never accepted it, and the message expired.Temporary
  3. 4.4.316Destination server refused the connection.Exchange Online is trying to deliver outside Microsoft 365, but every connection to the receiving server is being refused.Temporary
  4. 4.5.3Too many recipients from one domain.The message had more than 200 envelope recipients from the same domain, so Microsoft 365 asked the sending server to split it.Temporary
  5. 4.7.850–899Temporary restriction on the sending IP.Microsoft 365 detected suspicious activity on the sending IP and is restricting it temporarily while it evaluates the traffic.Temporary
  6. 421 [RP-001]Outlook.com rate limit for the sending IP.Outlook.com is limiting how fast your IP can send to it because of the IP or domain's reputation; it is temporary and your server should retry.Temporary
  7. 421 [RP-002]Outlook.com rate limit on this connection.Your IP has sent more over a single connection than Outlook.com allows, a limit Microsoft ties to IP and domain reputation.Temporary
  8. 421 [RP-003]Outlook.com connection limit.Your IP has opened more connections to Outlook.com than it is allowed, a limit Microsoft links to IP and domain reputation.Temporary
  9. 421 4.3.240HVE: too many simultaneous connections.A High Volume Email sender opened more than 250 simultaneous authenticated connections, so Exchange Online closed the extra ones.Temporary
  10. 432 4.3.2Recipient mailbox is receiving too fast.Exchange Online is slowing delivery to one mailbox because it is receiving too many messages at once; the sending server should retry later.Temporary
  11. 450 4.4.244HVE: recipient rate limit exceeded.An HVE account sent many messages to a small number of recipients in a short time, and Exchange Online throttled the submission.Temporary
  12. 450 4.4.317Remote server sends an incomplete certificate chain.During the TLS handshake the other server sent only its own certificate, and Exchange Online could not verify it against a trusted root.Temporary
  13. 450 4.7.26IPv6 mail without an SPF or DKIM pass.Microsoft 365 refused a message that arrived over IPv6 because the sender passed neither SPF nor DKIM.Temporary
  14. 451 4.7.500–699Temporary IP throttling.Microsoft 365 is deferring mail from the sending IP because its traffic changed sharply; the restriction lifts once the traffic looks legitimate.Temporary

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