For security reasons, you are required to use encryption for accessing
email (IMAP) and sending outgoing email (SMTP).
For IMAP, set the port to 993 and click on the "Use SSL" or "Use
secure connection (SSL)" check box.
For SMTP, click on the "Use Secure Sockets Layer (SSL)" check
box or the "TLS" radio button under "Use secure connection:"
and make sure the port is set to 587.