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Common Email Bouncebacks

A bounceback message generates when there is an issue with the sending or receiving mail server. The bounceback error typically gives us some insight into what the problem is. Below is a categorized list of potential bounceback errors and their meanings. 


Quota/Limit Related Bounceback Message (Incoming)

Bounceback MessageReason/MeaningResolution
SMTP 421 (Server Temporarily Not Available)Temporary fail because our mail queue is too full.Try sending the email at a later time.
SMTP 550 ("fromemail" max messages per session)Too much mail was sent at once. Email limits exceeded.Try sending the email at a later time.

Receiver Account-Related Bounceback Message (Incoming)

Bounceback MessageReason/MeaningResolution
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 as the account is using greylisting.
SMTP 550 ("fromemail" sender rejected)Email address isn't properly formatted (has no @domain).Make sure you entered the correct email address. It should be properly formatted.
SMTP 550 ("toemail" recipient rejected GL/BL)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.Remove the invalid email address from the email.

Content-Related Bounceback Message (Incoming)

Bounceback MessageReason/MeaningResolution
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 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.Removed the 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.Put an option to opt-out in your email messages. Check the sending lists to ensure correct recipients. If the message was flagged erroneously, save a copy of the original email and report it to us.
SMTP 552 (virus-infected message rejected)Sender attached something a file format that our server does not allow (.bat .btm .cmd .com .cpl .dll .exe .lnk .msi .pif .prf .reg .scr .vbs).Put an option to opt-out in your email messages. Check the sending lists to ensure correct recipients. If the message was flagged erroneously, 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 that your email is spam, or that your IP has been blacklisted. 

Common Outgoing Bounceback Message

Bounceback MessageReason/MeaningResolution
Reject connection SMTP 554 (rejected for policy reasons)Was blacklisted or detected as most likely being spam. The recipient server has doubts about the sender’s authenticity or the sender’s 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, 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. Additionally, it is advisable to whitelist your email address on the recipient's end and our mail server hostname in their spam filter. Apart from this, it is necessary to 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. Email limits exceeded.Have them try sending the email at a later time.
SMTP 550 ("fromemail" sender rejected - ERR082)The sender is blocked for spam, blacklist, 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. Additionally, it is advisable to whitelist your email address on the recipient's end and our mail server hostname in their spam filter. Apart from this, it is necessary to resend the email and check if it gets delivered.
SMTP 550 ("fromemail" sender rejected - ERR081)Domain is blacklisted.This is most probably because the receiver blocks your domain which resulted in the email not going through. Suggest getting the domain name whitelisted at the receiver's end.
SMTP 550 ("fromemail" suspect invalid mailer domain, please check your dns records - ERR006)The 'From' email is sent as an IP address.Validate your 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. Make sure that all records are up to date. And try to whitelist the email and try again.
SMTP 550 ("fromemail" Suspect invalid mailer domain, please check your DNS records - ERR007)No A or MX records.Validate your 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. Make sure that all records are up to date. And try to whitelist the email and try again.
SMTP 550 ("fromemail" Suspect invalid mailer domain, please check your DNS records - ERR008)If DNS check fails.Validate your 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. Make sure that all records are up to date. And try to whitelist the email and try again.
SMTP 550 ("fromemail" Suspect invalid mailer domain, please check your DNS records - ERR009)Invalid A or MX record.Validate your 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. Make sure that all records are up to date. And try to whitelist the email and try again.
SMTP 550 ($toemail recipient is invalid - ERR010)The 'To' email is an IP address.Confirm the email address with the cx and ask to verify the spelling of it. Suggest him to retry sending.
SMTP 550 ($toemail recipient is invalid - ERR011)Recipient DNS check fails.Validate your existing DNS Records. This could be an issue with misconfiguration of DNS, an SPF or DKIM Record is not allowing the emails to be received, or blacklisting of the email address/domain. Make sure that all records are up to date. And try to whitelist the email and try again.
SMTP 550 ($toemail recipient is invalid - ERR013)The recipient domain is not a fully qualified domain name.Confirm the email address with the cx and ask to verify the spelling of it. Suggest him to retry sending.
SMTP 550 ($toemail recipient is invalid - ERR014)The email recipient is not a valid email address/domain.Confirm the email address with the cx and ask to verify the spelling of it. Suggest him to retry sending.
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.
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.
Validate your 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. Make sure that all records are up to date. And try to whitelist the email and try again. 
UCE ( Unsolicited Commercial E-Mail ) strictly prohibitedThe recipient is sending unsolicited e-mail to any person or persons the sender does not know or have prior explicit consent to send the message(s) to. 

Basic Troubleshooting Guide

  1. Check the existing Inbound Filtering policies that the email may have violated.
  2. Check if the email address is in the Blacklist and if the sender can be trusted, add it to the Approved Senders list. Please note that this option is not yet available in the Foundation dashboard. 
  3. Make sure that the recipient of the email you are sending is valid.
  4. Check the IP address of your mail server to see if the receiving domain is blocking it.
  5. Contact the receiving domain and see if they have any policy restrictions or blacklists that may be causing the bounced emails.
  6. Monitor your email storage.


NOTE: For IP rotation and for further assistance, please do not hesitate to reach our customer service.
 

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