At the Email Client Software (Outlook) change the authentication in your account settings from "Clear Text Authentication" to other option.

Step:1
# vim /etc/dovecot/conf.d/10-auth.conf

# allow plain text auth

        disable_plaintext_auth = no

# allowed authentication mechanism, at least these 2 options

        auth_mechanisms = plain login

Save & Exit

Step:2
Restart dovecot

  # /etc/init.d/dovecot                restart