With the FREE verison you can't use MAPI, EWS, EAS, CYREN and Message Sniffer.
And you can't do FAILOVER.
Read here for more details:
Gabriele Maoret - Head of SysAdmins at SERSIS
Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)