If you just want to get Dovecot running with typical configuration in a typical environment, here's what you'll have to do:
If you compiled and installed Dovecot from sources, Dovecot has installed only a /usr/local/etc/dovecot/README file, which contains the path to the installed example configuration files, usually /usr/local/share/doc/dovecot/example-config. Copy the dovecot.conf file and conf.d directory from the example-config directory into /usr/local/etc/dovecot/. Prebuilt packages usually install the configuration files directly into /etc/dovecot/.
You'll find the path by running doveconf -n | head -n 1.
It's a good idea to read through all the files and see what settings you might want to change.
auth required pam_unix.so account required pam_unix.so
You can let Dovecot do its automatic mail location detection, but if that doesn't work, you can set the location manually in mail_location setting. See MailLocation for more information.
Make sure that all software accessing the mboxes are using the same locking methods in the same order. The order is important to prevent deadlocking. From Dovecot's side you can change these from mbox_read_locks and mbox_write_locks settings. See MboxLocking for more information.
If you're using /var/mail/ directory for INBOXes, you may need to set mail_privileged_group = mail so Dovecot can create dotlocks there.
For better performance you may want to set mbox_very_dirty_syncs = yes option.
For better performance you may want to set maildir_copy_with_hardlinks = yes option (default in v1.1+).
Check imap_client_workarounds and pop3_client_workarounds and see if you want to enable more of them than the defaults.
If you're going to use Dovecot's POP3 server, you'll need to add pop3 to protocols line in the dovecot.conf file.
You'll also have to set pop3_uidl_format setting. If you're migrating from another POP3 server, see migration page. Otherwise set it to Dovecot v1.1+'s default:
pop3_uidl_format = %08Xu%08Xv
SSL and Plaintext Authentication
If you intend to use SSL, set ssl_cert and ssl_key settings. Otherwise set ssl = no. Easiest way to get SSL certificates built is to use Dovecot's doc/mkcert.sh script. See SSL.
By default Dovecot doesn't allow users to send passwords unencrypted to the server. Usually if SSL is enabled, it's a good idea not to allow this. However, if you don't offer SSL for some reason, you'll probably want to set disable_plaintext_auth = no.
To enable imaps and pop3s, make sure they have a inet_listener with ssl = yes in conf.d/master.conf's service imap-login and service pop3-login.
If you're using NFS or some other remote filesystem that's shared between multiple computers, you really should be using Dovecot v1.1 or later. See NFS for more information about what settings you'll need to change and what other issues you'll have to be aware of.
If you have only a single Dovecot server, or if the users almost always log into same physical server, you may want to consider storing the indexes into local disks instead. This is done by appending :INDEX=path to mail_location. For example:
mail_location = maildir:~/Maildir:INDEX=/var/indexes/%u
Remember that if you're storing indexes locally you can keep mmap_disable = no and mail_nfs_index=no (which gives better performance).