Via POP3 accounts - the easy way (PostMasterPOP3.pl)
OTRS is able to receive emails from POP3 accounts.
Configure your POP3 accounts via the admin interface (POP3 Account).

Execute bin/PostMasterPOP3.pl and all emails will be fetched to your OTRS system.
There is also an example cronjob (var/cron/postmaster_pop3.dist) which execute
your bin/PostMasterPOP3.pl every 10 minutes (see also chapter cronjobs).