Set up Exchange 2010 with Dynamic IP

Hi All,

We have the following problem with our MS Exchange Server 2010

The following is how we have set it up so far:

1. Installed Server 2008 R2 Enterprise x64
2. Ran DC Promo
3. Installed all prerequisites for exchange 2010
4. Installed Exchange 2010 Hub transport onto SERVER1
5. Installed Edge Role on SERVER2
6. Configured Accepted Domains to include all
7. Configured Send + Receive Connectors

Problem is

1. We can only send + receive mails internally.
2. We have a dynamic IP with our ISP and it changes daily

How can we configure our server to solve the problems

Any help will be appreciated

Thanks