These messages:
Running services check warning -- A non-Scalix IMAP service is enabled at this run level. You must disable this before trying to run Scalix server.
Running services check failed -- A non-Scalix IMAP service is already running. You must stop it before starting Scalix server.
Running services check failed -- A non-Scalix POP3 service is already running. You must stop it before continuing.
usually means dovecot is installed and running. Dovecot is installed and enabled by default in RHEL/CentOS. To correct this you need to stop the dovecot service. I'd recommend you also uninstall the dovecot package. It's not needed by Scalix and if it does ever start while Scalix is running, will cause problems.
Best regards,
Fred