Exchange and Internet Mail Service

Recently I inherited the Ms exchange Admin job when our existing Admin left right after blowing away our MS Exchange system. I was able to re-install and recover the message stores for everyone, but still not sure if Internet Mail Service is setup correctly. Our company name is 1234.com, but we receive/send our internet email from an ISP (deltacom.net).
How do I setup the IMS to receive/send email in the connector? Our company uses Outlook at the client workstations and exchange info pretty regularly. This is somewhat confusing right now.

Thanks,
Jolley_watson@bellsouth.net