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The transaction failed permanently. The server will not try to send the message again. This is used as a general error code, so there are many reasons why you could be seeing it. It’s common for email service providers to add a status code (5.1.1) after the SMTP reply code (smtp;550) for additional categorization of the issue.
7 responses for SMTP 550
smtp;550 5.1.1 The email account that you tried to reach does not exist. Please try double-checking the recipient's email address for typos or unnecessary spaces. Learn more at https://support.google.com/mail/?p=NoSuchUser - gsmtp
Gmail says this mailbox does not exist. Treat it as a hard bounce and remove the address.
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 - gsmtp
Gmail says this mailbox is disabled. Suppress it if it keeps failing.
smtp;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
Gmail permanently rate-limited this recipient. Confirm the address was not list-bombed, then suppress it if delivery never recovers.
smtp;550 5.7.1 [x.xx.xx.xx] Our system has detected that this message is likely suspicious due to the very low reputation of the sending domain. To best protect our users from spam, the message has been blocked. Please visit https://support.google.com/mail/answer/188131 for more information. - gsmtp
Gmail permanently blocked this for low domain reputation. Check Postmaster Tools, fix authentication, and pause volume until reputation recovers.
smtp;550 5.7.1 [x.xx.xx.xx] Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail, this message has been blocked. Please visit https://support.google.com/mail/?p=UnsolicitedMessageError for more information. - gsmtp
Gmail permanently blocked this as unsolicited mail. Review consent, engagement, and complaint rates before sending again.
smtp;550 5.7.1 Unauthenticated email from example.com is not accepted due to domain's DMARC policy. Please contact the administrator of example.com domain if this was a legitimate mail. Please visit https://support.google.com/mail/answer/2451690 to learn about the DMARC initiative. - gsmtp
Gmail rejected this under the domain DMARC policy. Align SPF or DKIM with the From domain so DMARC passes, then resend.
smtp;550 5.7.1 [x.xx.xx.xx 14] Messages missing a valid address in From: header, or having no From: header, are not accepted. - gsmtp
Gmail rejected a missing or invalid From header. Fix the From name and address formatting, then resend.
1 responses for SMTP 550
smtp;550 relaying denied for <example@example.com>
Yahoo denied relaying for this address. Authenticate properly and send only to accepted recipients.
4 responses for SMTP 550
smtp;550 5.1.1 <example@icloud.com>: user does not exist
iCloud says this mailbox does not exist. Check for typos, then remove it if it is still wrong.
smtp;550 5.7.1 [CS01] Message rejected due to local policy. Please visit https://support.apple.com/en-us/HT204137
Apple blocked this under a local filter policy. Follow Apple's sender guidance, then contact their postmaster with logs if it persists.
smtp;550 5.7.1 Your message was rejected due to example.com’s DMARC policy. See https://support.apple.com/en-us/HT204137 for info
Apple rejected this under your domain DMARC policy. Align SPF or DKIM with the From domain so DMARC passes, then resend.
smtp;550 5.7.1 Your email was rejected due to having a domain present in the Spamhaus DBL -- see https://www.spamhaus.org/dbl/
Apple rejected a URL that appears on the Spamhaus DBL. Delist the domain with Spamhaus, then wait for caches to refresh before retrying.
4 responses for SMTP 550
smtp;550 5.1.1 Not our Customer
Comcast says this is not their customer. Treat it as a hard bounce and remove the address.
smtp;550 5.1.1 <example@comcast.net> recipient mailbox unallocated
Comcast says this mailbox is unallocated. Treat it as a hard bounce and remove the address.
smtp;550 5.2.0 Message rejected due to DMARC. Please see http://postmaster.comcast.net/smtp-error-codes.php#DM000001
Comcast rejected this under DMARC. Align SPF or DKIM with the From domain so DMARC passes, then resend.
smtp;550 5.2.0 <example@comcast.net> - Recipient unavailable
Comcast says this recipient is unavailable. Verify the address. Suppress it if it keeps failing.
4 responses for SMTP 550
smtp;550 5.5.0 Requested action not taken: mailbox unavailable. [#.eop-nam12.prod.protection.outlook.com]
Outlook says the mailbox is unavailable. Verify the address. Remove it if it stays undeliverable.
smtp;550 5.7.1 Service unavailable, MailFrom domain is listed in Spamhaus. To request removal from this list see https://www.spamhaus.org/query/lookup/ (S8002) [#.eop-nam02.prod.protection.outlook.com]
Outlook blocked the MailFrom domain on Spamhaus. Delist with Spamhaus, then wait for caches to refresh before retrying.
smtp;550 5.7.1 Unfortunately, messages from [x.xx.xx.xx] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [#.eop-nam02.prod.protection.outlook.com]
Outlook blocked part of your provider network. Slow volume and work with your ESP or ISP on the block list entry until it expires.
smtp;550 5.4.1 All recipient addresses rejected : Access denied [#.eop-nam02.prod.protection.outlook.com]
Outlook denied access for all recipients on this host. Ask the recipient admin to allowlist your sender if the mail is legitimate.
3 responses for SMTP 550
smtp;550 Message was not accepted -- invalid mailbox. Local mailbox example@mail.ru is unavailable: account is disabled
Mail.ru says this mailbox is disabled. Suppress it if it keeps failing.
smtp;550 spam message rejected. Please visit http://help.mail.ru/notspam-support/id?c=7y4ytdHbuOGv3O50NYTwpz1F-TVIpnactxtFPeFQSDYMAAAAaKgAAOX_3hE~ or report details to abuse@corp.mail.ru. Error code: ###. ID: #
Mail.ru rejected this as spam. If you rarely send there, check signup forms for bot abuse. Otherwise clean content and list quality.
smtp;550 Message was not accepted -- invalid mailbox. Local mailbox example@mail.ru is unavailable: account is disabled
Mail.ru says this mailbox is disabled. Suppress it if it keeps failing.
2 responses for SMTP 550
smtp;550 5.7.1 Policy rejection on the target address
Yandex blocked the recipient account for policy violations. Suppress the address.
smtp;550 5.7.1 No such user!
Yandex says this user does not exist. Treat it as a hard bounce and remove the address.
3 responses for SMTP 550
smtp;550 5.2.1 <EXAMPLE@PRODIGY.NET>... Addressee unknown, relay=[x.xx.xx.xx]
AT&T says the addressee is unknown. Treat it as a hard bounce and remove the address.
smtp;550 5.2.1 <example@prodigy.net>... blank mailhost - invalid address, relay=[x.xx.xx.xx]
AT&T rejected this as an invalid address. Treat it as a hard bounce and remove it.
smtp;550 5.7.1 Connections not accepted from servers without a valid sender domain. ## Fix reverse DNS for x.xx.xx.xx
AT&T requires a valid sender domain and reverse DNS on the sending IP. Fix the PTR record, wait for propagation, then resend.
2 responses for SMTP 550
smtp;550 5.7.1 Email rejected per DMARC policy for zoho.com
Zoho rejected this under DMARC for a zoho.com From address. Send through Zoho SMTP settings, or stop using that From on an external ESP.
smtp;550 5.1.1 <example@zoho.com> User unknown
Zoho says this mailbox does not exist. Treat it as a hard bounce and remove the address.
4 responses for SMTP 550
smtp;550 spam detected
Free.fr marked the message as spam. Clean content and formatting, then retry only if the send is legitimate.
smtp;550 5.2.2 user quota exceeded
This Free.fr mailbox is over quota. Retry later, or ask the recipient to free space.
smtp;550 5.2.1 This mailbox has been blocked due to inactivity
This Free.fr mailbox is blocked for inactivity. Suppress it until the recipient reactivates the inbox.
smtp;550 virus detected
Free.fr detected a virus in the message. Scan the content and attachments, remove the threat, then resend a clean copy.
2 responses for SMTP 550
smtp;550 Requested action not taken: mailbox unavailable
GMX says the mailbox is unavailable. It may not exist or may be disabled for inactivity. Verify spelling, then suppress if it stays dead.
Requested action not taken: mailbox unavailable Reject due to policy restrictions.
GMX rejected this for policy reasons, often weak reputation or non-compliant headers. Fix authentication and RFC header issues, then retry carefully.
1 responses for SMTP 550
smtp;550 5.1.1 Email address could not be found, or was misspelled (G8)
Rackspace could not find this mailbox. Treat it as a hard bounce and remove the address.
1 responses for SMTP 550
smtp;550 5.7.1 Rejected by spam filter (in reply to end of DATA command)
Proton Mail rejected this above its spam threshold. Trim risky content and links, then resend a cleaner message.
1 responses for SMTP 550
smtp;550 5.7.1 Message considered as SPAM
ImprovMX rejected this as spam. Trim risky content and links, then resend a cleaner message.
7 responses for SMTP 550
smtp;550 Mail is rejected by recipients
QQ rejected this under the recipient filter or personal blacklist. Contact the recipient another way if the mail is legitimate.
smtp;550 Mailbox unavailable or access denied
QQ temporarily blocked sends to this recipient after a flood of mail. Wait and retry later.
smtp;550 Mailbox not found. http://service.exmail.qq.com/cgi-bin/help?subtype=1&&id=20022&&no=1000728
QQ says this mailbox was not found. Treat it as a hard bounce and remove the address.
smtp;550 Mail content denied. http://service.exmail.qq.com/cgi-bin/help?subtype=1&&id=20022&&no=1000726
QQ denied the message content as bulk spam. Rewrite the content and improve list quality before trying again.
smtp;550 Sender frequency limited. http://service.exmail.qq.com/cgi-bin/help?subtype=1&&id=20022&&no=1000723
QQ rate-limited this sender. Slow volume and wait out the window before sending again.
smtp;550 Suspected spam sender.
QQ flagged the domain or operator as a suspected spam source. Clean list quality and reputation before retrying.
smtp;550 DMARC check failed http://service.mail.qq.com/cgi-bin/help?subtype=1&&no=1001508&&id=16.
QQ rejected this under DMARC. Align SPF or DKIM with the From domain so DMARC passes, then resend.
1 responses for SMTP 550
smtp;550 5.1.1 <example@hey.com>: Recipient address rejected: User unknown
Hey says this mailbox does not exist. Check for typos, then remove it if it is still wrong.
1 responses for SMTP 550
smtp;550 5.7.1 rejected by DMARC policy for example.com (in reply to end of DATA command),
Infomaniak rejected this under DMARC. Align SPF or DKIM with the From domain so DMARC passes, then resend.
1 responses for SMTP 550
smtp;550-SPF-check failed: 550 example.com doesn't allow sending mails from xx.xx.xx.xx (in reply to MAIL FROM command)
Hostpoint rejected this because SPF failed for the sending IP. Add the sending server to the domain SPF record, then resend.
3 responses for SMTP 550
smtp;550 5.2.0 Mail rejete. Mail rejected. ofr_506 [506]
Orange rejected the message. Review content, authentication, and recent complaint rates before retrying.
smtp;550 5.1.1 Adresse d au moins un destinataire invalide. Invalid recipient. OFR_416 [416]
Orange says at least one recipient is invalid. Fix or remove the bad address, then resend.
smtp;550 mwinfXXXX ME Adresse IP source bloquee pour incident de spam. Client host blocked for spamming issues. OFR006_102 Ref http://csi.cloudmark.com/reset-request/?ip=xxx.xxx.xxx.xxx [102]
Orange blocked your IP through Cloudmark Sender Intelligence. Request delisting, then retry after the block clears.
10 responses for SMTP 550
smtp;550 <example@example.com>: Reject due to SPF policy. The originating IP of the message is not permitted by the domain owner
Web.de rejected this because SPF failed for the sending IP. Publish a correct SPF record that includes your sending servers.
smtp;550 <example@example.com>: Syntax error in parameters or arguments
Web.de refused reception due to incorrect server configuration. Fix SMTP setup with your admin, then retry.
smtp;550 <example@example.com>: Requested action not taken: mailbox unavailable
Web.de says the mailbox is unavailable. It may not exist or may be disabled for inactivity. Verify, then suppress if it stays dead.
smtp;550 <example@example.com>: Bad DNS PTR resource record
Web.de rejected your IP for a bad PTR record. Set a proper reverse DNS hostname for the sending IP, then resend.
smtp;550 <example@example.com>: Reject due to policy restrictions (header based)
Web.de rejected the message for header policy problems. Fix Date, From, Sender, and To headers so they are unique and RFC-valid.
smtp;550 <example@example.com>: Reject due to policy restrictions (domain based)
Web.de rejected the sender domain under security policy. Improve domain reputation before sending again.
smtp;550 <example@example.com>: Reject due to policy restrictions (IP based)
Web.de temporarily blocked your IP after too much spam-like traffic. Pause volume and clean engagement before retrying.
smtp;550 <example@example.com>: Requested mail action aborted: exceeded storage allocation, Quota exceeded
This Web.de mailbox is over quota. Retry later, or ask the recipient to free space.
smtp;550 <example@example.com>: IP address is block listed
Your IP is on a block list used by Web.de. Delist it, then retry after caches refresh.
smtp;550 <example@example.com>: Invalid DNS MX or A/AAAA resource record
Web.de could not find a valid MX or A record for your domain. Publish working mail DNS so replies and bounces can land.
5 responses for SMTP 550
smtp;550 Administrative prohibition - envelope blocked - https://community.mimecast.com/docs/DOC-1369#550 [#]
Mimecast blocked the envelope under an administrative prohibition. Ask the recipient admin to allow your sender if the mail is legitimate.
smtp;550 Rejected by header based Anti-Spoofing policy: email@example.com - https://community.mimecast.com/docs/DOC-1369#550 [#]
Mimecast anti-spoofing blocked this, often when To and From share a domain but the send goes through an ESP. Adjust spoofing policy or routing with the admin.
smtp;550 Rejected by header based manually Blocked Senders: email@example.com - https://community.mimecast.com/docs/DOC-1369#550 [#]
Mimecast blocked this sender on a manual block list. Ask the recipient admin to remove the block if the mail is legitimate.
smtp;550 Envelope blocked - User Entry - https://community.mimecast.com/docs/DOC-1369#550 [#]
This Mimecast customer blocked your envelope for their domain only. Ask that admin to allowlist you. It is not a global Mimecast ban.
smtp;550 DMARC Sender Invalid - envelope rejected - https://community.mimecast.com/docs/DOC-1369#550 [#]
Mimecast rejected this because SPF failed for the Return-Path domain. Publish all sending IPs in SPF, then resend.
13 responses for SMTP 550
smtp;550 5.1.1 <email@example>: Recipient address rejected: User unknown
Proofpoint says this user is unknown. Treat it as a hard bounce and remove the address.
smtp;550 5.1.1 <email@example.com>: Recipient address rejected: undeliverable address: host example.com[x.xx.xx.xx] said: 550 5.1.1 <email@example.com>: Recipient address rejected: user unknown
Proofpoint quoted a downstream user-unknown reject from the final mail server. Treat it as a hard bounce and remove the address.
smtp;550 5.1.1 User Unknown
Proofpoint says this user is unknown. Treat it as a hard bounce and remove the address.
smtp;550 5.1.1 - This is not a valid email address. Please verify that you have the correct email address for your recipient.
Proofpoint says this is not a valid email address. Verify spelling, then remove it if it stays wrong.
smtp;550 5.1.8 <sender@example.com>: Sender address rejected: Domain not found (in reply to RCPT TO command)
Proofpoint rejected the sender domain because it was not found. Make sure From and Return-Path domains exist and can receive mail.
smtp;550 5.1.8 Domain of sender address does not exist
Proofpoint says the sender domain does not exist. Make sure From and Return-Path domains exist and can receive mail.
smtp;550 5.5.2 <email@example.com>: Sender address rejected: need fully-qualified address (in reply to RCPT TO command)
Proofpoint needs a fully qualified sender address. Fix From and Return-Path to use real domains, then resend.
smtp;550 5.7.0 Email rejected per sender's DMARC policy
Proofpoint rejected this under the sender DMARC policy. Align SPF or DKIM with the From domain so DMARC passes, then resend.
smtp;550 5.7.1 <email@example.com>: Recipient address rejected: User email address is marked as invalid.
Proofpoint marked this recipient address as invalid. Suppress it unless the recipient confirms a corrected address.
smtp;550 5.7.1 Relaying denied
Proofpoint denied relaying. The recipient may not be a customer, or you are not allowed to use this relay. Send only to accepted recipients.
smtp;550 5.7.1 Relay access denied
Proofpoint denied relay access. The recipient may not be a customer, or you are not allowed to use this relay.
smtp;550 5.7.1 Service unavailable; client [x.xx.xx.xx] blocked using prs.proofpoint.com
Proofpoint blocked your IP on its dynamic reputation list. Request delisting, then retry after the block clears.
smtp;550 5.7.1 Service unavailable; client [x.xx.xx.xx] blocked using Cloudmark Sender Intelligence (Visit http://csi.cloudmark.com/reset-request/ if you feel this is in error)
Proofpoint blocked your IP through Cloudmark Sender Intelligence. Request delisting, then retry after the block clears.
4 responses for SMTP 550
smtp;550 5.4.1 [email@example.com]: Recipient address rejected: Access denied [example.com]
Exchange Online denied access for this recipient. Often the address is invalid. Confirm with their mail admin if you believe it should work.
smtp;550 5.7.1 Service unavailable, Client host [x.xx.xx.xx] blocked using Spamhaus. To request removal from this list see https://www.spamhaus.org/query/ip/0.0.0.0 (AS16012611)
Exchange Online blocked your sending IP on Spamhaus. Delist with Spamhaus, then wait for caches to refresh before retrying.
550 5.7.1 Service unavailable, Helo domain is listed in Spamhaus. To request removal from this list see https://www.spamhaus.org/query/lookup/ (S8001) [#.prod.protection.outlook.com]
Exchange Online blocked the HELO domain on Spamhaus. Match HELO to your forward DNS, delist if needed, then retry after caches refresh.
smtp;550 5.7.606 Access denied, banned sending IP [x.xx.xx.xx]. To request removal from this list please visit https://sender.office.com/ and follow the directions. For more information please go to http://go.microsoft.com/fwlink/?LinkID=526655 (AS16012609)
Exchange Online banned this sending IP. Submit a removal request at sender.office.com, then pause volume until the ban lifts.
5 responses for SMTP 550
smtp;550 cuda_nsu 5.1.1 <email@example.com>... User unknown
Barracuda says this user is unknown. Treat it as a hard bounce and remove the address.
smtp;550 No such user (email@example.com)
Barracuda says there is no such user. Treat it as a hard bounce and remove the address.
smtp;550 Blocked
Barracuda blocked delivery because the mailbox was unavailable or rejected by policy. Verify the address. Ask the recipient admin if it should be allowed.
smtp;550 rejecting spoofed message
Barracuda thinks this message spoofs a known brand. Check From details, domains, and links for unintended brand signals, then resend a cleaner copy.
smtp;550 permanent failure for one or more recipients (email@example.com:blocked)
Barracuda permanently failed this recipient as blocked for content or domain reasons. A different message may still deliver later.
1 responses for SMTP 550
smtp;550 Invalid recipient <email@example.com> (#5.1.1)
Email Security.cloud says this recipient is invalid. Treat it as a hard bounce and remove the address.
1 responses for SMTP 550
smtp;550 5.7.1 <example@example.com>: Recipient address rejected: ERS-Customized-Block.
Trend Micro's Email Reputation System blocked this under a custom filter. Ask the recipient admin to review the ERS rule if the mail is legitimate.
1 responses for SMTP 550
smtp;550 5.7.26 <example@example.com>: ETP205 DMARC Failure for domain
FireEye rejected this for DMARC failure. Align SPF or DKIM with the From domain so DMARC passes, then resend.
Response catalog adapted from the MIT-licensed SMTP Field Manual by ActiveCampaign / Postmark.
