How to enable Email Client Mailing system on PoP server

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