If an attempt to send to an email address results in a hard bounce or 4 or more soft bounces in a 3 month period, we will automatically add that email address to a blocked list and will not send to it again. If you believe that the address is still valid, you can remove the address from the blocked list via the relevant Excluded Recipient record.
Goals
- Learn how to unblock and email address
- Learn why an email address would become blocked
- Learn what various bounce codes mean
How to Unblock an Email Address:
Begin by opening the sent Email Send on which the address was excluded, then scroll down to the Excluded Recipient subgrid and open the Excluded Recipient record for the address you want to unblock. Once the record is open, click the Unblock button.
This will open a pop-up window showing the address that you want to unblock and the reason why the address is blocked.
If you believe the address is still valid and you've read the reasons why it could be blocked (in this article below), check "I confirm this email address is correct and should be unblocked", then click the Unblock button. This will remove the email address from our blocked list and allow you to send emails to it again. Though this does not guarantee that the email will be successfully delivered as it may bounce again for the same or a different reason as the first time.
Why an Email Address will be Blocked:
Invalid Recipient: An Invalid Recipient bounce reason indicates that the email address is not valid. Either the address has been abandoned, it never existed, or there is a typo. You will want to validate the address with the recipient and send them an email successfully through your email client (Outlook) before unblocking.
DNS Failure: A DNS Failure bounce reason can sometimes indicate that there is a temporary technical issue but most of the time it indicates an issue with the domain. Either the domain is no longer in use or there is a typo within the domain. You will want to validate that the domain is active and used for email before unblocking.
Soft Bounce: A Soft Bounce reason indicates that the email address had 4 soft bounces in a rolling 90-day period. Soft bounces sometimes indicate a temporary issue but if an email persistently has a soft bounce it typically indicates a more permanent issue. You’ll want to look at the bounce message to determine the issue and correct it before unblocking.
With all bounce types its important to note that repeated bounces will cause sender reputation issues. You will want to verify the email address is correct and address any other issues before unblocking. The best was to determine the issue is to look at the bounce message that was sent back from the recipient’s email server.
How to Find Out More Information About Why the Email Bounced:
NOTE: Bounce types, messages, and error codes are not standardized. This means bounce types and messages can vary across mail servers even for the same issue. To view the bounce message, you’ll need to view the Email Events for an Email Send. Our help article on Email Events will show you how to get there.
Invalid Recipients Invalid Recipient addresses are where the domain is a valid email domain but the account (inbox) does not exist.
Message examples:
- smtp;550 5.1.1 Recipient not found
- smtp;550 5.1.1 Recipient address rejected: User unknown
- smtp;550 unknown user account
DNS Failures DNS Failure addresses are where the domain is invalid, no longer in use, or does not have MX records associated with it (a domain needs MX records to be able to send and accept email). There are a lot of cases where a DNS Failure will not have a bounce message.
If DNS Failure bounces are received en masse and across several different domains, it may indicate a temporary issue with the DNS server.
Message examples:
- Status = 5.4.4 (unable to route: no mail hosts for domain) | Diag =
- Status = 5.1.2 (bad destination system: no such domain) | Diag =
- Status = 4.4.4 (unable to route: dns lookup failure) | Diag =
Soft Bounces Soft Bounces encompass a broad range of issues. Usually soft bounces are described as temporary but that is not always the case. With this type of bounce, the message sent back is especially important in figuring out a root cause.
Message examples with possible explanations:
- smtp;554 5.4.6 Hop count exceeded - possible mail loop
- Mail loop and hop issues on are the recipient side
- smtp;452 4.2.2 The email account that you tried to reach is over quota
- The recipient’s mailbox is full
- smtp;5.1.1 - Bad destination email address 'reject' (delivery attempts: 0)
- The email account that you tried to reach is disabled.
- smtp;550 5.7.1 Recipient rejected (R4)
- Invalid recipient email address (even though its returned as a soft bounce)
- smtp;550 Denied by policy
- Could be a SPF failure or any other rule set up on the receiving mail server; mail bounced by spam filter
- smtp;554 5.7.1 This email has been rejected. The email message was detected as spam.
- The content of the message, IP, or domain is causing email to be flagged as spam
- smtp;554 5.1.0 Sender denied
- smtp;550 Rejected
- The sending domain has been blocked for the recipient or email identified as spam
- smtp;550 5.7.1 Command not allowed
- smtp;550 Mail could not be processed
- smtp;550 5.5.0 Service refuse. Veuillez essayer plus tard. service refused, please try later.
- These could indicate that there is a temporary issue with the mail server