Understanding Bounce-Back Emails: Types, Causes, and Solutions
Bounce Back Email Meaning
A bounce-back email is a message a sender will receive if the email they sent was not delivered successfully to the recipient. In the message, there is an error that will help identify the problem.
In this article, we will discuss the different types of bounce back emails and how to troubleshoot them. Please select from the options below for more information:
- Mail Quota/Limit Errors on Incoming Messages
- Account-Related Errors on Incoming Messages
- Content-Related Errors on Incoming Messages
- Errors in Outgoing Messages
- Best Practices to Prevent Bounce-Back Emails
- Review
Mail Quota/Limit Errors on Incoming Messages
Understand the meaning of each error below and what to do about bounce-back emails.
| Bounce-Back Emails | Meaning | Resolution |
|---|---|---|
| SMTP 421 (Server Temporarily Not Available) | Temporary fail because our mail queue is too full. | Try sending the email later. |
| SMTP 550 ("fromemail" max messages per session) | Many emails were sent at once, exceeding our email limits. | Try sending the email later. |
Account-Related Errors on Incoming Messages
Learn how to fix the bounce-back email errors in the table below.
| Bounce-Back Emails | Meaning | Resolution |
|---|---|---|
| SMTP 452 ("toemail" requested action aborted: try again later - GL/GL) | Temporary failure. The account is using greylisting and will be accepted when the delivery is retried. |
Retry sending the email. |
| SMTP 550 ("fromemail" sender rejected) | The email address is not properly formatted. |
Make sure you correctly enter the email address ([email protected]). |
| SMTP 550 ("toemail" recipient rejected GL/BL) | Permanent failure. The recipient blacklisted the sender. |
Try to contact the recipient by other means to remove the block. Your email address could have been blacklisted by accident. |
| SMTP 550 ("toemail" recipient rejected) | The email address you are sending to doesn't exist. | Remove the invalid email address and confirm the correct email address. |
Content-Related Errors on Incoming Messages
Discover the resolution to each of the errors listed below.
| Bounce-Back Emails | Meaning | Resolution |
|---|---|---|
| SMTP 421 (Temporary Rejection. Reverse DNS for "IP" failed) | SMTP Temporary rejection - Couldn't identify the PTR record. |
Verify if the sending IP Address has a reverse DNS setup before resending an email. |
| SMTP 552 (Remote MTA $ip: A URL contained in this message is blacklisted by Spamhaus DBL. See http://www.spamhaus.org/dbl) | A URL in the body is blacklisted. |
Remove the invalid URL from the body of the email and send it again. |
| SMTP 552 (virus-infected message rejected) | Cloudmark detected the message as having a virus. | Include an opt-out option in your email messages. Check the sending lists to ensure the recipients are correct. If the message was flagged in error, save a copy of the original email and report it to us. |
| SMTP 552 (virus-infected message rejected) | The sender attached something in a file format our server does not allow (.bat .btm .cmd .com .cpl .dll .exe .lnk .msi .pif .prf .reg .scr .vbs). | Include an opt-out option in your email messages. Check the sending lists to ensure the recipients are correct. If the message was flagged in error, save a copy of the original email and report it to us. |
| SMTP 554 (Connection refused - "IP") | This is rejected for spam based on CSI. |
Check Cloudmark Sender Intelligence (CSI) to see the current reputation of the sending IP Address. |
| SMTP 554 (Connection Rejected. Reverse DNS for "IP" does not exist) | Permanent rejection. They don't have a PTR record. |
The incoming server perceives your email as spam or that your IP has been blacklisted. |
Errors in Outgoing Messages
Below are common errors you may see for outgoing messages and their solutions.
| Bounce-Back Emails | Meaning | Resolution |
|---|---|---|
| Reject connection SMTP 554 (rejected for policy reasons) | Blacklisted or detected as being spam. The recipient server has doubts about the sender’s authenticity or message. |
Review and check if the IP address is listed on the Spamhaus Policy Block List. |
| Reject SMTP 550 ($toemail recipient rejected - ERR016) | The recipient is blocked for spam, blacklist, or email limit purposes. |
Contact the sender to check the server logs on their end to know the exact reason for the rejection of the email. The recipient should whitelist your address and our mail server hostname in their spam filter. Then, resend the email and check if it gets delivered. |
| SMTP 452 ("fromemail" sender rejected. Too many messages for this connection ERR034) | Too much mail was sent at once, exceeding the email limits. |
Try sending the email later or send fewer messages at a time. |
|
SMTP 550 ("fromemail" sender rejected - ERR082) |
The sender is blocked for spam, blacklist, or email limit purposes. |
Contact the sender to check the server logs on their end to know the exact reason for the rejection of the email. The recipient should whitelist your address and our mail server hostname in their spam filter. Then, resend the email and check if it gets delivered. |
| SMTP 550 ("fromemail" sender rejected - ERR081) | The domain is blacklisted. |
This is likely because the recipient blocked your domain name, resulting in the email not going through. Ask the recipient to whitelist the domain name. |
| SMTP 550 ("fromemail" suspect invalid mailer domain, please check your DNS records - ERR006) | The 'From' email is sent as an IP address. |
Check your existing DNS Records. This could be an issue with misconfiguration of DNS, an SPF or DKIM Record not allowing the emails to be received, or blacklisting of the email address/domain. Make sure that all records are up-to-date. Try whitelisting the email and try again. |
| SMTP 550 ("fromemail" Suspect invalid mailer domain, please check your DNS records - ERR007) | No A or MX records. |
Check your existing DNS Records. This could be an issue with misconfiguration of DNS, an SPF or DKIM Record not allowing the emails to be received, or blacklisting of the email address/domain. Make sure that all records are up-to-date. Try whitelisting the email and try again. |
| SMTP 550 ("fromemail" Suspect invalid mailer domain, please check your DNS records - ERR008) | The DNS check failed. |
Check your existing DNS Records. This could be an issue with misconfiguration of DNS, an SPF or DKIM Record not allowing the emails to be received, or blacklisting of the email address/domain. Make sure that all records are up-to-date. Try whitelisting the email and try again. |
| SMTP 550 ("fromemail" Suspect invalid mailer domain, please check your DNS records - ERR009) | Invalid A or MX record. |
Check your existing DNS Records. This could be an issue with misconfiguration of DNS, an SPF or DKIM Record not allowing the emails to be received, or blacklisting of the email address/domain. Make sure that all records are up-to-date. Try whitelisting the email and try again. |
| SMTP 550 ($toemail recipient is invalid - ERR010) | The 'To' email is an IP address. |
Confirm the email address, including verifying the spelling. Retry sending. |
| SMTP 550 ($toemail recipient is invalid - ERR011) | Recipient DNS check fails. |
Check your existing DNS Records. This could be an issue with misconfiguration of DNS, an SPF or DKIM Record not allowing the emails to be received, or blacklisting of the email address/domain. Make sure that all records are up-to-date. Try whitelisting the email and try again. |
| SMTP 550 ($toemail recipient is invalid - ERR013) | The recipient domain is not a fully qualified domain name. |
Confirm the email address, including verifying the spelling. Retry sending. |
| SMTP 550 ($toemail recipient is invalid - ERR014) | The email recipient is not a valid email address/domain. |
Confirm the email address, including verifying the spelling. Retry sending. |
| Error 550: You have reached the maximum number of messages per session. | The IP address has reached the maximum number of messages allowed for that particular session. |
Try sending the email later. |
| Reported error: 550 The Domain Name System (DNS) reported that the recipient's domain does not exist |
The recipient's domain does not exist. The recipient has no MX records. The recipient has no A record for the mail server. |
Check your existing DNS Records. This could be an issue with misconfiguration of DNS, an SPF or DKIM Record not allowing the emails to be received, or blacklisting of the email address/domain. Make sure that all records are up-to-date. Try whitelisting the email and try again. |
| UCE (Unsolicited Commercial Email) strictly prohibited | The recipient is sending unsolicited email to any person or persons the sender does not know or have prior explicit consent to send the message(s) to. |
Best Practices to Prevent Bounce-Back Emails
- Verify email addresses before sending. Check if the email address is on the blacklist. If the sender can be trusted, add the email address to approved senders (also called safe listing or whitelisting).
- Make sure that the recipient’s email address is valid and spelled correctly.
- Check the IP address of your mail server to see if the receiving domain is blocking it.
- Contact the receiving domain and see if they have any policy restrictions or blacklists that may be causing the bounced emails.
- Check your DNS/ADNS records to confirm the configuration is correct.
- Monitor your email storage.
Review
Bounce-back emails can happen on a personal account as well as a business email account. Understand different error messages related to mail quota/limit, account-related issues, content-related errors, and outgoing messages. For each bounce back email, specific SMTP codes are discussed together with their meanings and resolutions, ranging from temporary failures due to full mail queues or greylisting to permanent rejections due to incorrect email formats, blacklisting, or policy violations. Best practices to prevent bounce back emails include timely resolution of these errors by retrying email delivery, correcting email addresses, removing invalid URLs, and whitelisting email addresses or domains.