I have a base Zoho account. I can login to the Zoho site. I can receive mail. I can’t send mail. I used to be able to send and receive mail. I have not changed my settings. I can’t send mail on both Apple Mail on an iPad and MS Outlook. Settings are

username@Anonymous User 

Attempting to send mail fails,  no such address. I can, I repeat, receive mail at this address.

is there a problem that I should know about?