From time to time you might send an email out and find you receive an email bounce back with an obscure message as the error in the message.
Below is a table of the possible messages, what they mean and a solution.
| SMTP Error | Explanation | Solution |
|---|---|---|
| Host or domain name not found. MX host not found. | There are no MX records for the recipient's domain | This message will not be delivered. The recipient must create MX records with their DNS host so that they can receive email. |
| 450 4.1.8: Sender address rejected: Domain not found | The recipient is unable to verify the existence of your domain. | First, verify you have spelled the email address correctly. Then verify the domain part of the email is correct. |
| 451 4.3.0: Client host rejected: Throttled - Too much spam from your mail server. Try again later. | The recipient’s server has received too much spam from this source. | Try sending the message again later. Ask the recipient to Safelist/Whitelist your domain. |
| 451 4.3.0: Temporary lookup failure | An intermittent issue has occurred. | The receiving mail server experienced an internal issue. Typically, it will resolve itself. Wait a few minutes, then try sending the message again. |
| 421: Too many concurrent connections from this client (G2) | The sending IP has too many concurrent connections with our servers. | The receiving mail server is receiving too much mail. Try again later, or reduce the number of messages you're sending to this recipient. |
| 4.4.1: The recipient's server was temporarily unavailable to accept your message (G6) | When your domain is Split Domain Routing enabled and the recipient’s address (hosted on the external mail server) soft fails. | The message will be deferred to be resent at a later time. Ensure the external mail server is up and running and accepting connections over port 25 (SMTP). |
| 504 5.5.2: Sender address rejected: need fully-qualified address | The domain you are sending from is not valid. | You must use a valid domain for sending emails. |
| 550: Your message has been rejected because you have been detected sending spam. | The content of this message has been deemed spam by the internet community. | Spam definitions change rapidly. Try changing the subject or removing any strange characters or images. |
| 550 5.1.0: Sender address rejected: User unknown in relay recipient table | Your domain exists, but the full email address you have sent from does not. | Create the address in the form of a mailbox, list, or alias to send mail from. |
| 550 5.1.1: Recipient address rejected: User unknown in relay recipient table | The recipient’s email address does not exist in the hosted domain. | Add an email address to the hosted domain. |
| 550 5.7.1: Relay access denied | This error usually indicates that the address you are sending to does not exist or there is an issue with the recipient domain’s DNS configuration. | Check the recipient's address for any misspellings/typos. Resend the message. |
| 550 5.3.4: Message too large (G17) | The message exceeded the maximum message size allowed by our servers (75 megabytes). | The sender will need to ensure the message size is under the allowed threshold and re-send the message. |
| 550 5.7.0: [blocked file] - Your message has been rejected because it contains a banned file attachment (G1A) | The message contains an attachment file type that is blocked. | Remove the banned file type and re-send. |
| 550 5.7.0: [blocked file] - Your message has been rejected because it contains a banned file attachment (G1B) | The message contains an attachment file type that is blocked. | Remove the blocked file type and re-send. |
| 550 5.7.0: [blocked file] - File attachment is not allowed because they can be used to exploit Winzip (G1C) | The message contained an attachment that can be used to exploit WinZip-associated files:.b64; .bhx; .hqx; .mim; .uue?; .xxe | Remove the banned file type and re-send. |
| 554 5.7.1: Client host rejected: The sender's mail server is blocked | Sending IP is blocked internally | Safelist IP and/or send domain/address. |
| 5.7.1: ACL dns_rbl; Client host [XX.XX.XX.XX] blocked using Spamhaus PBL. Please visit http://www.spamhaus.org/lookup/ for more information on why this message could not be delivered (G1)|The sending server is blacklisted by Spamhaus's PBL. | The sending server is blacklisted by Spamhaus’s PBL. | The sender needs to follow the link http://www.spamhaus.org/lookup/ to request remediation from Spamhaus’s blacklist. Safelisting the sender will NOT allow an exception. The only solution is for the sender to get the IP removed from Spamhaus. |
| 554 5.7.1: ACL dns_rbl; Client host [XX.XX.XX.XX], blocked using sa-ip4tset.blagr.emailsrvr.com=127.26.0.2 Cloudmark CSI. Please visit http://csi.cloudmark.com/reset-request for more information on why this message could not be delivered | The sending server is blacklisted by Cloudmark. | The sender needs to follow the link http://csi.cloudmark.com/reset-request to request remediation from Cloudmark’s blacklist. The recipient can Safelist the sender in the meantime. |
| 5.7.1: ACL dns_rbl; Client host [XX.XX.XX.XX],blocked using sa-ip4tset.blagr.emailsrvr.com=127.22.0.2 Senderscore. Please visit https://senderscore.org/rtbl/ for more information on why this message could not be delivered | The sending server is blacklisted by Senderscore. | The sender needs to follow the link https://senderscore.org/rtbl/ to request remediation from Senderscore’s blacklist. The recipient can Safelist the sender in the meantime. |
| 5.7.1: ACL dns_rbl; Client host [XX.XX.XX.XX], blocked using sa-ip4tset.blagr.emailsrvr.com=127.24.0.2 Spamhaus XBL. Please visit http://www.spamhaus.org/lookup/ for more information on why this message could not be delivered | The sending server is blacklisted by Spamhaus’s XBL. | The sender needs to follow the link http://www.spamhaus.org/lookup/ to request remediation from Spamhaus’s blacklist. The recipient can Safelist the sender in the meantime |
| 5.7.1: ACL dns_rbl; Client host [XX.XX.XX.XX],blocked using sa-ip4tset.blagr.emailsrvr.com=127.23.0.2 Spamhaus SBL. Please visit http://www.spamhaus.org/lookup/ for more information on why this message could not be delivered | The sending server is blacklisted by Spamhaus’s SBL. | The sender needs to follow the link http://www.spamhaus.org/lookup/ to request remediation from Spamhaus’s blacklist. The recipient can Safelist the sender in the meantime (link safelist). |
| 5.7.1: ACL dns_rbl; Client host [XX.XX.XX.XX],blocked using sa-ip4tset.blagr.emailsrvr.com=127.5.0.X Spamcop. Please visit http://spamcop.net/bl.shtml for, more information on why this message could not be delivered | The sending server is blacklisted by Spamcop. | The sender needs to follow the link http://spamcop.net/bl.shtml to learn more about Spamcop’s blacklist. If Spamcop receives no other spam reports from that IP within 24 hours, the IP is removed. The recipient can Safelist the sender in the meantime. |
| 554 5.7.1: Sender address rejected: Blocked by this domain | The sender is blacklisted at the domain level | Remove the sender from the domain-level blacklist. or safelist at the recipient level. |
| 554 5.7.1: Sender address rejected: Blocked by this recipient | The sender is blacklisted at the user level. | Remove the sender from the user-level blacklist. |
| 554 5.5.2: Invalid data in message #SMTP# | The name of the attached document is longer than 50 characters. | To correct this, shorten the name of the document you are sending. |
| 550 5.7.1: <${user@example.com}>: The recipient's server refused to accept your message (G7) | Occurs when a domain has Split Domain Routing enabled and the recipient’s address (hosted on the external mail server) permanently fails | Confirm that the recipient’s address does in fact exist on the external server (check for misspellings) and re-send the message. |
| 550 5.1.1: <${user@example.com}>: Email address could not be found or was misspelled (G8) | Occurs when the recipient address (and domain) does not exist on our system. | Check the recipient’s address for any potential misspellings/typos. Resend the message. |
| 550 5.1.1: <${user@example.com}>: Email address could not be found or was misspelled (G9) | Occurs when the recipient address (and domain) does not exist on our system. | Check the recipient's address for any potential misspellings/typos. Resend the message. |
| 550 5.7.1: Email rejected per DMARC policy for [XXXXXXX] (G15) | The sender failed DMARC; has a DMARC policy of “reject”. | Have the sender verify the sending source and make sure it is compliant with their DMARC policy. It may also be necessary for them to update their DMARC DNS record. The sender will need to re-send the message. |
| 550 5.7.23: The message was rejected because of Sender Policy Framework violation | The sender failed the SPF policy, and the policy is set to reject. This error can also occur when a message is automatically forwarded or sent as your domain from a webform. | Verify the sending domain has the SPF TXT record setup correctly on their domain name. e.g. v=spf1 include:emailsrvr.com ~all Review our DNS setting guides. |