Problem with receiving emails

Hello mailsac, I tried to send an email from my gmail to an inbox of mailsac, nothing came to the inbox, instead showed the attached message


Why is that?

Hello Mohammad,

I’m discussing your issue with our engineering team. I will follow up with you.

Michael

Here’s server response if it helps:
The response from the remote server was:
421 Message to [email protected] temporarily deferred for 121 seconds, upgrade for better performance