Additionally, you may disable IMAP and POP3 servers. This is the service which delivers the email to your inboxes while exim is the one which sends the mails to the servers. So both Exim and Courier ( or Dovecot ) is essential for the proper functioning of the email service in a cpanel server.
To select or disable a mail server:
- Select Courier, Dovecot, or Disabled.
- If you wish to preserve users’ mailbox settings (such as subscriptions and information about which messages have been read), click the Convert mailbox settings… checkbox.
- Click Save.
Courier is the traditional IMAP server installed by cPanel, and is extremely reliable. Being reliable, courier have a larger memory foorprint. Courier doesn’t index the maildir where the mail is stored, so every time you open up the webmail client it has to reaload the entire inbox, which makes it a bit slower to load compared to dovecot, when we are dealing with large mailboxes.
However, Dovecot uses less memory, provides better performance, and is more configurable. Dovecot is much faster than Courier due to the indexing it provides. One big advantage of Dovecot is its intelligent use of configuration files, whereas Courier tends to spread them all over the system. Additionally Dovecot uses maildir format so is compatible with standard Courier installations, so, if you ever wish to convert to dovecot, you can without affecting the mailbox.
So, if you are running a shared server, dovecot can deliver better performance while you have a dedicated server for one or two websites, courier can be more efficient. The default choice for cPanel is the dovecot and if you need to change it to courier, you may need to navigate to WHM Main >> Service Configuration >> Mailserver Selection.