Quick note here -

If you are installing Exchange 2007 or Exchange 2010 and are in an environment where your local domain is different that your public domain, you might run into an issue getting your Outlook Clients to connect when they are not on the network.

There is a quick and easy fix to this, though.  Open a powershell session and enter the following commands:

Get-ExchangeCertificate

This will give you the information on the certificates that are being used.  Find the one that is being used for the public connections and copy the thumbprint number.

Then type the following:

Enable-ExchangeCertificate -Thumbprint XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX -Services "SMTP"

(where the XX's are the number copied from the previous command)

<span style="color: #000000">Th</span>is enables the RPC services to use the certificate when connecting outside of the local network.