[Dovecot] Outlook client timeouts on sending mail

This may be a sendmail question, but I thought I'd ask here first: I set up an Outlook client to use secure IMAP and secure SMTP. When sending a message, the client typically times out once or twice and presents an error message indicating the server isn't configured for secure delivery. With a little persistence, Outlook eventually makes a successful connection, and the message goes on its way (2-3 tries).

Any pointers as to where to look for the problem?

Thanks, Jay