Unable to send message; & Sorry, we are unable to process your request.

Unable to send message; & Sorry, we are unable to process your request.

Hi, I am unable to send mail every time I do I get "Unable to send message;"
This is happening on both my desktop and my mobile app.

Also whilst trying to update the send as section in case of any password or setting errors I get "Sorry, we are unable to process your request."

This is business critical, as this is my main work email! HELP!