Unable to send message;

Unable to send message;

Hi,

I've been using Zoho Mail for about a year.  Everything went smoothly until about a week ago.  For some reason, I get this error message when attempting to send an email: 

"Unable to send message;"

Nothing else is specified.  Has anyone had a similar issue?


I've attached screenshots of some settings in case that helps narrow down the problem



Cheers,

-Greg