Starting from the upcoming 0.2.5 update, all new installations of OpenPanel Enterprise edition will include a mailserver.

summary:

0.2.5 - adds mailserver only for outgoing mail from php websites
0.2.6 - adds terminal commands to create/manage email accounts
0.2.7+ - will add gui pages for both admin and users to manage emails

php.ini files are automatically edited to allow websites to send email without any configuration.

The version after that, 0.2.6 will allow Administrators to create/manage email accounts, and users to access them via webmail.

OpenPanel users will still not have any interface to manage emails, and have access only to webmail of your choosing: Roundcube, SnappyMail or sogo. All email accounts are created/managed only via terminal.

Users emails are stored in /home/$USERNAME/mail/$DOMAIN/$EMAIL directories - same as on other panels.

New terminal commands that will be available from 0.2.6 for OpenPanel Enterprise users:

opencli email-server

opencli email-server <install|start|restart|stop|uninstall>

opencli email-webmail

opencli email-webmail <roundcube|snappymail|sogo>

opencli email-setup

opencli email-setup help
opencli email-setup email add <EMAIL ADDRESS> [<PASSWORD>]
opencli email-setup email update <EMAIL ADDRESS> [<PASSWORD>]
opencli email-setup email del [ OPTIONS... ] <EMAIL ADDRESS> [ <EMAIL ADDRESS>... ]
opencli email-setup email restrict <add|del|list> <send|receive> [<EMAIL ADDRESS>]
opencli email-setup email list

opencli email-setup alias

opencli email-setup alias add <EMAIL ADDRESS> <RECIPIENT>
opencli email-setup alias del <EMAIL ADDRESS> <RECIPIENT>
opencli email-setup alias list

opencli email-setup quota

opencli email-setup quota set <EMAIL ADDRESS> [<QUOTA>]
opencli email-setup quota del <EMAIL ADDRESS>

opencli email-setup dovecot-master

opencli email-setup dovecot-master add <USERNAME> [<PASSWORD>]
opencli email-setup dovecot-master update <USERNAME> [<PASSWORD>]
opencli email-setup dovecot-master del [ OPTIONS... ] <USERNAME> [ <USERNAME>... ]
opencli email-setup dovecot-master list

opencli email-setup config

opencli email-setup config dkim [ ARGUMENTS... ]

opencli email-setup relay

opencli email-setup relay add-auth <DOMAIN> <USERNAME> [<PASSWORD>]
opencli email-setup relay add-domain <DOMAIN> <HOST> [<PORT>]
opencli email-setup relay exclude-domain <DOMAIN>

opencli email-setup fail2ban

opencli email-setup fail2ban 
opencli email-setup fail2ban ban <IP>
opencli email-setup fail2ban unban <IP>
opencli email-setup fail2ban log
opencli email-setup fail2ban status

opencli email-setup debug

opencli email-setup debug fetchmail
opencli email-setup debug login <COMMANDS>
opencli email-setup debug show-mail-logs

After the 0.2.6 version, we will focus on creating interfaces for users to manage email accounts:

list/add/modify/delete email accounts
autologin to webmail
list/add/modify/delete forwarders/filters/autoresponders
view email summary and limits for account
imapsync email import from another server

and for administrators as well:

configure webmail
view/edit configuration
view email sending summary and limits for users