Exchange 2007 receive problem

You will want to ensure the IP address your MX record was changed to, is able to forward your inbound mail to the Exchange server.
If it is a small firewall, you will want to make sure it forwards incoming SMTP to the internal address of your server.
Otherwise, if you have a pool of public IP addresses, you would be better assigning a static translation on your firewall of one of the pool of addresses, to the internal address of your Exchange server.
You would then want to ensure you allow SMTP through, obviously.
Regards.

You said:
"I had my email host provider move my MX record of Northernpharmacy.com to point towards my firewall"
What did the original MX record point to? Is this Exchange server a new installation or one that was working OK before?

C:\Documents and Settings\netman>nslookup
Default Server: sbs1.****.local
Address: 10.1.82.1
> set type=mx
> northernpharmacy.com
Server: sbs1.****.local
Address: 10.1.82.1
Non-authoritative answer:
northernpharmacy.com MX preference = 10, mail exchanger = exchange2007.northe
rnpharmacy.com
exchange2007.northernpharmacy.com internet address = 63.139.89.78
> exit

C:\Documents and Settings\netman>telnet 63.139.89.78 25
220 exchange2007.northernpharmacy.com Microsoft ESMTP MAIL Service, Version: 6.0
.3790.3959 ready at Thu, 17 Jul 2008 09:56:48 -0400
ehlo sbs1.****.com
250-exchange2007.northernpharmacy.com Hello [*.*.19.3]
250-TURN
250-SIZE 2097152
250-ETRN
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-8bitmime
250-BINARYMIME
250-CHUNKING
250-VRFY
250 OK
mail from:
250 2.1.0 postmaster@****.com....Sender OK
rcpt to:
550 5.7.1 Unable to relay for blichtig@northernpharmacy.com
quit
221 2.0.0 exchange2007.northernpharmacy.com Service closing transmission channel
Connection to host lost.
C:\Documents and Settings\netman>