SMTP Server Dovecot / Exim Authentication error

Recently, I've installed the centOS 6. The purpose of the installation to use this server as Mail server. Where I've installed **Exim version 4.84_2 #1** and **Dovecot**. I've followed this blog post and I've tried to solve the below given error, however I do not have luck to resolve it. 2017-02-06 07:07:27 no host name found for IP address x.x.x.x 2017-02-06 07:07:32 dovecot_plain authenticator failed for ([x.x.x.x]) [x.x.x.x]: 535 Incorrect authentication data (set_id=mailclown@com-supportnet.work) 2017-02-06 07:07:40 dovecot_plain authenticator failed for ([x.x.x.x]) [x.x.x.x]: 535 Incorrect authentication data (set_id=mailclown@com-supportnet.work) 2017-02-06 07:07:48 dovecot_login authenticator failed for ([x.x.x.x]) [x.x.x.x]: 535 Incorrect authentication data (set_id=mailclown@com-supportnet.work) 2017-02-06 07:07:52 dovecot_login authenticator failed for ([x.x.x.x]) [x.x.x.x]: 535 Incorrect authentication data (set_id=mailclown@com-supportnet.work) Following is the output the configuration which I used from the above blog post. [root@com-supportnet ~]# dovecot -n # 2.0.9: /etc/dovecot/dovecot.conf # OS: Linux 2.6.32-642.11.1.el6.x86_64 x86_64 CentOS release 6.8 (Final) auth_mechanisms = plain login auth_socket_path = /var/run/dovecot/auth-userdb mail_location = maildir:~/mail mbox_write_locks = fcntl passdb { driver = pam } service auth { unix_listener auth-client { mode = 0777 user = exim } } ssl_cert = /etc/ssl/mail.com-supportnet.work.crt ssl_key = /etc/ssl/mail.com-supportnet.work.key userdb { driver = passwd } Please let me know, how I can resolve this error.