An error occurred inside the server which prevented it from fulfilling the request.

I use firefox on my desktop PC and never had this issue.  I cannot send an email using my secondary email as the sender through my primary email portal.  I also tried MS Edge and got the same error.  I then went into my security setting and unchecked the third party security login out, then logged back in and re-checked it.  Still no luck on the send.  Please help.  FYI: I can send from my iphone.  Go figure.