This list of instructions will set up all the directories necessary for imap. You are now the user cyrus. This is necessary for the files to have the correct owner and group. You are now root again. Postfix is a mail-deliver alternative to sendmail.
Most linux installations use sendmail by default.
Then the setup has been successful. Setting up users Still as the user cyrus, type the following commands. If you don't periodically prune the database of deliveries, you can fill up your file system. Adding a cron job which will run once a day is one way to do this.