Spammers often have dirty mailing lists, containing large numbers of invalid recipient addresses. If MailChannels detects that a sender has been sending to large numbers of invalid recipients recently, the sender may be blocked with the [BBD] error code.
What can I do to unblock the sender?
If the sender is delivering messages to a mailing list, please verify that the addresses in the list are valid. You can use a tool such as http://www.verifyemailaddress.org/ or http://mailtester.com/testmail.php for address verification.
Generally speaking, to avoid the [BBD] error, senders should
- Reduce the number of invalid recipients on their mailing lists by using a confirmed opt-in process, consistent with M3AAWG Sender Best Practices.
- Remove invalid recipients from their lists immediately.
- Only send to subscribers who have opted in to their lists.
MailChannels automatically stops generating the [BBD] error when the frequency of invalid recipients falls to a normal level. Note that we do not use a specific threshold of invalid recipients, and cannot therefore advise on a specific permissible rate of invalid recipients.