Postfix
Main config file /etc/postfix/main.cf, with only 2 lines:
mydestination = khmel.org
home_mailbox = Maildir/
Create user test:
useradd test
Email for test@khmel will be in /var/mail/test.
Courier
POP3. Courier will look to /home/test/Maildir to check directories: cur, new, tmp and file courierpop3dsizelist.
Creating directories for user test:
cd /home/test
maildirmake Maildir
chown -R test.test Maildir