That's a quite involved problem, as it could be any number of mis-configurations, mail server blocks, etc.
Since you have an Olympus Pro product, your dealer is obligated to provide
customer service (although it may not be free - we're fairly unique in providing free installation for our customers). They should be able to check the configurations on both ends of the situation and make the appropriate adjustments.
Sorry to say, but the configuration of a DS-4000 system is not clear-cut or easy. It's not necessarily Olympus' fault, as anytime you deal with e-mail it can be difficult. Personally, we prefer FTP for transfers: much easier, faster and safer than e-mail.
Sorry we can provide a more complete answer, but there are much too many things to discuss in one simple posting.
Good luck.