If you or a user is getting this error message, it means the sender of the message has been identified as sending email messages to a large number of invalid recipient addresses recently. Our system automatically blocks senders who attempt delivery to a large number of invalid recipients in a short period of time, because this behavior is often indicative of spamming.
What can I do to unblock the sender?
The sender needs to verify that most of the email addresses they send to are valid.
Best practices to avoid this problem include the following steps:
- Reduce the number of invalid recipients on your list by ensuring that every recipient on the list has given clear consent via an opt-in step. Never send bulk email to a recipient address who has not previously given consent to you.
- Remove invalid recipients from your list immediately. You will always have some invalid addresses due to people changing email addresses, but the lower the number, the better your reputation.
Once the mailing list is cleaned up and the number of invalid addresses goes down, you will be able to send mails automatically without any intervention from MailChannels.