What does the mailbox response “No MX for [RecipientEmailDomainName]” mean?

The error reading "No MX for [RecipientEmailDomainName]" usually indicates an issue with the recipient’s domain. This can affect some or all recipients with the domain indicated in the mailbox response so we recommend checking with your IT department to see if they encountered any issues with your mail service provider the day the original message was sent.

Once you remove any individuals from the bounce/spam list you can use the Resend to Failed Recipients procedure (found in the Action menu of the sent email record) to resend the email to those who did not receive it initially.