SMTP code 550 is a permanent failure notice, typically indicating that the
recipient's email address is invalid or unavailable. This error is commonly
encountered when the recipient's mailbox does not exist or the domain is
not hosted on this SMTP server.
It may also be due to policy restrictions such as blocked senders or
disabled accounts. In many cases a failure to provide SPF, DKIM or other
verification / authentication methods can result in this error.
Each digit in an SMTP response code carries a specific meaning.
Permanent Negative
The command failed permanently. Do not retry without changes.
Mail System
Status of the mail system as a whole.
Specific Condition
The third digit narrows the response. Zero is typically generic; higher values are increasingly specific.
Typical server responses you may encounter.
550 5.1.1 <[recipient email]>: Recipient address rejected: User unknown
550 5.1.1 <[recipient email]>: user does not exist
550 Requested action not taken: mailbox unavailable
550 5.4.1 Recipient address rejected: Access denied.
550 Rejected by header based manually Blocked Senders: [email address]
550 #5.1.0 Address rejected.
550 This domain is not hosted here
550 Mailbox is full / Blocks limit exceeded / Inode limit exceeded
550 Invalid Recipient - [Link]
550 5.2.1 <[recipient email]>... User's mailbox is disabled
550 Message was not accepted -- invalid mailbox. Local mailbox [email address] is unavailable: user is terminated
550 unrouteable address
550 5.4.1 Recipient address rejected: Access denied. [Server details]
550 5.2.1 <[recipient email]>... Addressee unknown, relay=[IP address]
550 Email blocked by [Blocklist]
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.
550 5.2.1 The email account that you tried to reach is disabled.
550 5.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered.
550 5.4.5 Daily sending quota exceeded.
550 5.4.5 Daily SMTP relay limit exceeded for user.
550 5.7.0 Mail relay denied.
550 5.7.0 Mail Sending denied. This error occurs if the sender account is disabled or not registered within your Google Workspace domain.
550 5.7.1 Email quota exceeded.
550 5.7.1 Invalid credentials for relay.
550 5.7.1 Our system has detected an unusual rate of unsolicited mail originating from your IP address. To protect our users from spam, mail sent from your IP address has been blocked. Review Prevent mail to Gmail users from being blocked or sent to spam.
550 5.7.1 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
550 5.7.1 The IP you're using to send mail is not authorized to send email directly to our servers. Please use the SMTP relay at your service provider instead.
550 5.7.1 The user or domain that you are sending to (or from) has a policy that prohibited the mail that you sent. Please contact your domain administrator for further details.
550 5.7.1 Unauthenticated email is not accepted from this domain.
550 5.7.1 Daily SMTP relay limit exceeded for customer.
550 5.7.26 Unauthenticated email from [domain-name] is not accepted due to domain's DMARC policy.
550 5.7.26 This message does not have authentication information or fails to pass authentication checks (SPF or DKIM). To best protect our users from spam, the message has been blocked.
550 5.7.26 This message fails to pass SPF checks for an SPF record with a hard fail policy (-all). To best protect our users from spam and phishing, the message has been blocked.
Why you might receive this response.
To address a 550 error:
Need help with email delivery?
CloudMailin can help troubleshoot and resolve SMTP issues.
SMTP code 421 indicates a temporary issue with the server that prevents it from processing requests
SMTP code 450 is a generic temporary error and is used in a wide variety of conditions by the receiving server
SMTP code 451 indicates a temporary local error on the receiving server
SMTP code 452 is used to indicate that the recipient's email server is unable to accept the message due to a lack of storage space, too many recipients, or insufficient system resources
SMTP code 454 indicates an authentication issue, typically suggesting that the server is denying relay access due to a lack of proper authentication from the sender
SMTP code 455 is used to indicate a temporary issue with the server, where it suggests retrying the request at a later time
SMTP code 530 typically indicates that authentication is required to proceed with the requested email operation
SMTP code 550 is a permanent failure notice, typically indicating that the recipient's email address is invalid or unavailable
SMTP code 552 generally indicates a failure due to storage issues or a limit imposed by the recipient's mail server
SMTP code 553 is used to indicate a rejection due to the recipient's email address being invalid, typically in scenarios where the address is not recognized by the recipient's mail server
SMTP code 554 is a permanent failure notice, indicating that the message has been rejected and will not be delivered