Unable to send to HMC created Exchange 2007 mailbox user
from Exchange 2003 mailbox user in a co-existance

I have a co-existance Exchange Organization that consists of a single Exchange
2007 (M7) and Exchange 2003 (M5) servers in the HMC.

What is happening is this:

1. If I create a user on the exchange 2007 without HMC (using the Exchange Admin
tools) I can talk back and forth to exchange 2003 and external mail clients.

2. If I create a user on the exchange 2007 using HMC (using the webtools or
using scripts to create users) I cant send mail from exchange 2003 or send
emails out or in from external mail clients:  The error on the Exchange client
and external client is from M7...<m7.ictg.us #5.1.1 smtp;550 5.1.1
RESOLVER.ADR.RecipNotFound; not found>

3. If I move the mailbox back from Exchange 2007 (M7) to the exchange 2003 (M5)
server then it can talk like number 1, but HMC cant control the account.

There is something up with the HMC and how it creates accounts that corrupts or
doesnt allow the Organization within Exchange to see the recipient...

Does anyone have any suggestions to troublshoot as well as resolve?

Quick update:

Its confirmed, if I create a new user on Exchange 2007 then they cannot send
externally or recieve from outside or from exchange 2003 users.... so I was a
little off on the first post.

Looks like AD permissions problem. Check if both Exchange 2003/2007 servers has
proper access to new user account (At least Read, try to compare with a good
one).