Alpine SMTP error 421: "Error sending: Can not authenticate to SMTP Server: 421 SMTP connection broken (reply)"

Alpine SMTP error 421: "Error sending: Can not authenticate to SMTP Server: 421 SMTP connection broken (reply)"

Fri Feb 28 @ 9:20am EST.

Yesterday I was sending mail okay -- slow, but okay. Today, I am intermittently (frequently) receiving the error above. I have sent one or two small test emails successfully to another email account I own, but other emails I am sending to multiple (10) recipients are hitting this error.

I am configured to use:

smtp.zoho.com:465/user= john@mydomain.ca/ssl/submit

Please advise.

-john