SMTP Suddenly Died

Hi!

I am using the free mail service, without mail hosting.

Until a few days ago, I could send fine through SMTP. using smtp.zoho.com:587. Suddenly, I cannot send. When I use the test function of one of my programs, I get "The server response was 5.5.1, authentication required. I use my full email address as username, and the usual username.

Thanks.