New Exchange installation - not sending/receiving

We have been having HUGE issues with our Exchange Box over the last two days - and finally after an extensive weekend of backups and restores have been able to restore all mailboxes from PST's through EXMerge.
Our issue now is that we cannot send/receive email - internally...
The Exchange installation was the original one - it was just the mailbox store that was replaced etc.

Is there anything that we could have missed?
What is the usual cause for email not being able to be sent through an exchange server?

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What is your Internal domain name and what is the Internet domain name? If these are different, have you edited the domain name in the rcepient policy?
idsafsAuthor Commented:
The internal and internet domain names are different.
In the recipient policy it states:
smtp          @InternalDomain
SMTP         @InternetDomain

This was all working 100% on Friday, all I have done since then is configured a new mailbox store - and now we have this issue.
Is there anything in the Mailbox store that may be causing the issue?

Ok.i'm lost a bit. Is your IS mounted? Users can access their mailboxes though outlook or OWA?
Why you configurea new mailbox store, were you having problems before?
Questions that will help me to help you.
idsafsAuthor Commented:
The store is mounted, and we can access the mailboxes through OWA only.  
We have big issues with the old mailbox store - it was in a dirty shutdown state, and eseutil/p was failing to rectify - hence the new store.

Since yesterday we have done the following:
deleted all mailboxes again, uninstalled Exchange, uninstalled IIS (SMTP etc), reinstalled IIS, reinstalled Exchange.
Recreated all users mailboxes, and reimported their data from PST.
We are now able ot send and receive emails, internally and externally.

An issue that has reared now, is that my ISA box is "killing" the connections where I can see email trying to come through the box.  For some reason the exchange server is denying the connections.  DO you have any idea why this would be?  SHould I move this post?
YOu have two things that you have to make sure.
If your server is not a NAt client of ISA server (meaning the default gateway of your exchange server is not the ISA server, but a router on the network), in that case make sure that you have the option(Requests appear to come from the ISA server) checked within your SMTP server publishing rule on the To tab.
If your exchange servers default gateway is the ISA server, then you make sure that the option (Requests appear to come from the original client) is checked.

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