Common Email Bounce backs
A bounce back message is created when there is an issue with the sending or receiving mail server shortly after you have already sent the email(s) in question. The bounce back error typically provides some insight into what the problem is. Below is a categorized list of potential bounce back messages and their meanings.
Sender Account-Related
These errors all relate to your email address or account
Bounce back Message | Details | Resolution |
SMTP 550 ("fromemail" sender rejected) | Your email address isn't properly formatted (e.g. has no @domain). | Check your email setup and ensure that your from address is a valid email account.
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SMTP 550-5.7.26 this mail is unauthenticated | Email addressed from your domain is originating from an unauthorized source | Ensure that all legitimate sources of email for your domain are defined in your DNS SPF TXT record. |
SMTP 452 ("fromemail" sender rejected. Too many messages for this connection ERR034) | Too much mail was sent at once. Email limits exceeded. | Try sending fewer emails at once, at later time. |
SMTP 550 ("fromemail" max messages per session) | Too many mails were sent at once. Email limits exceeded. | Try sending fewer emails at once, at later time. |
Error 550: You have reached the maximum number of messages per session. | The IP address has reached the maximum allowed messages for that particular session. | Try sending the email at a later time. |
Receiver Account-Related
These errors all relate to the recipient's email address or account
Bounce back Message | Details | Resolution |
SMTP 550 ("toemail" recipient rejected) | Permanent failure. The sender is blacklisted at the user level (the customer blacklisted them). | Try to contact the receiver by other means. Your email address could have been blacklisted by accident. |
SMTP 550 ("toemail" recipient rejected) | The "To" mailbox doesn't exist. | Sometimes, an email address is mistyped causing a bounce back. Make sure you entered the correct email address. It should be properly formatted. |
SMTP 550 ($toemail recipient is invalid - ERR013) | The recipient domain is not a fully qualified domain name. | Confirm the email address you are sending to and verify the spelling of it. |
SMTP 550 ($toemail recipient is invalid - ERR014) | The email recipient is not a valid email address/domain. | Confirm the email address you are sending to and verify the spelling of it. |
Reported error: 550 The Domain Name System (DNS) reported that the recipient's domain does not exist |
| Ask the recipient to validate their existing DNS Records. This could be an issue with misconfiguration of DNS, an SPF or DKIM Record is not allowing the emails to be received, or blacklisting of the email address/domain. |
Reject SMTP 550 ($toemail recipient rejected - ERR016) | The recipient is blocked for spam, blacklist, email limit purposes. | You will also be unable to send emails to a server that has been blacklisted for spamming. The server will not be able to receive your mails and you will get a bounce back notification. |
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Content-Related
These errors all relate to the recipient's mail provider not liking some quality of your email.
Bounce back Message | Details | Resolution |
SMTP 552 (Remote MTA $ip: A URL contained in this message is blacklisted by [PROVIDER] | A URL in the body of your email is blacklisted. | Removed the URL from the body (or signature) of your email and send it again. |
SMTP 552 (virus-infected message rejected) | Server anti-virus detected the message as having a virus. | Check the content and attachments of your email. Perform virus scan as necessary to identify and correct source of infection |
SMTP 552 (virus-infected message rejected) | Server has rejected the email because of the risky file format attached. Some examples include: .bat .btm .cmd .com .cpl .dll .exe .lnk .msi .pif .prf .reg .scr .vbs | If the particular file(s) must be sent, consider using a zip program to zip them into an archive, and then attaching that arch (.zip file) to the email |
SMTP 554 (Connection refused - "IP") | This is rejected for spam based on the reputation of your IP address. | Perform a check on your IP address to see if/what blacklists it may be on. A reliable tool for checking can be found at https://mxtoolbox.com/blacklists.aspx |
Reject connection SMTP 554 (rejected for policy reasons) | You or your email were blacklisted or detected as most likely being spam. The recipient server has doubts about your authenticity or the message. | Perform a check on the IP address that appears in the message to see if/what blacklists it may be on. A reliable tool for checking can be found at https://mxtoolbox.com/blacklists.aspx |