I've had a number of questions regarding my previous post and questioning whether ISA is a requirement for our Push Email solution.
Let me clarify - it is NOT....
However.... there are some benefits of using ISA in that:
1) It'll pre-authenticate any SSL traffic
2) It will allow you to inspect the traffic passing through Port 443 and ensure it is Activesync traffic
Many customers won't have or won't want to implement ISA so you can use any firewall that allows you to publish port 443.