(HELP - PLEASE) Mail Delivery Status Notification (Delay) - Received this Message on two email accounts under the same domain with ZOHO.

(HELP - PLEASE) Mail Delivery Status Notification (Delay) - Received this Message on two email accounts under the same domain with ZOHO.

This message was created automatically by mail delivery system.


THIS IS A WARNING MESSAGE ONLY.


YOU DO NOT NEED TO RESEND YOUR MESSAGE.


    ----- The following addresses had fatal errors -----    

   [Status: Error, Address: <**@gmail.com>, ResponseCode 421, 4.7.0 Temporarily Deferred]

Message will be retried for 4 more day(s)


    ----- Transcript of session follows -----    

This has happened 2x today. Never before though.

Please Advise as to a solution. I plan on using my email address routed via mailchimp for a campaign in the coming weeks. If this is going to be an issue without solution, It would be best to know before I launch.