[CentOS] email Server for CentOS 7

[Kenneth Porter]

Read up on Postfix (SMTP) and Dovecot (POP3 and IMAP). (Sendmail is 
available as an alternative to Postfix.)

Additional services you'll want include MIMEDefang (general filter 
management), SpamAssassin (anti-spam), and ClamAV (anti-virus scanning).

Other useful services include OpenDKIM (validates that mail really came 
from the domain it claims to have come from), Roundcube (web-based email 
client),  and Certbot (acquire a LetsEncrypt cert for your mail servers). 
You might want OpenLDAP for authentication, identity management, and 
address books. Fail2ban can help keep the script kiddies out of your 
services.

Running a mail server requires knowledge of many different services and 
awareness of many security issues. You have your work cut out for you.