Zoho CRM emailing

Zoho CRM emailing

I was receiving an error "Could not convert to TLS" when trying to email contacts directly in Zoho CRM. My IT dept worked with Zoho and determined the issue was something on the exchange server, which is fixed. 

The mail server itself is only set up to accept the connection in general, not per user so we don’t understand why this is affecting some people and not others.

The initial error "Could not convert to TLS" now saying "535.5.7.3. Authentication Unsuccessful"

PLEASE HELP