Is the setting up of my mailserver all right?

hello, I followed this link to set up my mail server, pretty much I did every step except for the SSL certificate.

and I use this tool: http://mxtoolbox.com/SuperTool.aspx to do a smtp test and the results showed for SMTP Banner Check is "Reverse DNS FAILED! This is a problem. " and the session transcript showed “451 4.3.0 supertool@mxtoolbox.com: Temporary lookup failure [648 ms]”, other messages seemed fine.

I also used nmap to check the open ports and found pop3, smtp, pop3s and imamps all opened, meaning the server should be up now.

Is that all? Or I still configured it wrong? I was not able to use a mail client to get to my server though?

update:

after creating an account from a mail client, I tried to make a connection, and here is the /var/log/dovecot.log:

Jan 22 21:33:26 imap-login: Info: Disconnected (auth failed, 2 attempts in 8 secs): user=admin@entrepidea.com, method=PLAIN, rip=69.248.172.40, lip=104.131.223.35, TLS, session=<NwuDnEgNrwBF+Kwo> Jan 22 21:35:07 auth: Error: passwd-file: open(/etc/dovecot/dovecot-master-users-password) failed: Permission denied (euid=111(dovecot) egid=121(dovecot) missing +r perm: /etc/dovecot/dovecot-master-users-password, dir owned by 2000:121 mode=0750)

seemed that I need to chown the file…

Thanks, Jon