want to migrate from exchange

[sparzk]

scenario - i work with and use exchange, it works , but problematic when introduced to other mail servers. my school is made up of many of our own divisional smtp's. I DO want to dissolve my exchange and migrate the users in my particular domain to use the zimbra collaboration suite as it supports the calendering feature my faculty loves to use. my sister domain is supporting zimbra. the linux admin and I spoke about his security implements at the receiving end of his server.

my problem - the security features enabled by my sister domain are not letting me send sucessfully from my 2k7 exchange send connector, it stalls in the que and eventually it will NDR. I have DMZ capability and resolve using my interior dns MX record with "A" record pointer (from parent SOA ) that supplies FQDN for my exchange when it requests to send. I know several filters are enabled on the zimbra server. I know only basic exchange functions, so some of this is over my paygrade.

question - can zimbra email security filters deny and state that my HELO
communication is refused and my that my FQDN is invalid, if so what would
the email when returned look like in the diagnostic mode.

any help would be appreciated.

sparzk