Sending emails using dovecot auth

[Murray Trainer]

Hi All,

I have noticed that dovecot / exim on Cpanels appear to support
sending emails via exim after authenticating to Dovecot - see message
below

550-Please turn on SMTP Authentication in your mail client, or login
to the
550-IMAP/POP3 server before sending your message

We are migrating users mail off cpanels into split mta and dovecot
servers and are having problems with some users being abble to send
emails afterwards. 

Does anyone understand how the CPanel config works?

Thanks

Murray