Difference in External Domain name and Internal Domain name causing e-mail to fail in delivery.

I have a domain name called xxx-yy.com pointed to my external firewall IP. My internal domain is named xxxyy.com. I have been tasked with the job of implementing Exchange 2003 internally. (We have been using a hosted solution until now.)

I have installed and configured Exchange 2003 in domain xxxyy.com. This results in the users primary SMTP address as user1@xxxyy.com.
I have changed the MX records for domain name xxx-yy.com to point to my external firewall IP.
I have opened SMTP 25 and redirected traffic to my internal Exchange servers IP. (Tested successfully via telnet using mail.xxx-yy.com and user1@xxxyy.com)
I have added a second smtp address to each user account so they all have both user1@xxxyy.com and user1@xxx-yy.com addresses.
However, no mail is being delivered to the users accounts. Any guidance would be greatly appreciated.

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in edition to adding second smtp addresses to users' profiles, you have to add the domain to the recipients policy. EST -> site name -> recipients -> recipient policies -> double click  default recipient policy -> email addresses policy
add new @xxx-yy.com

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sorry EST, I meant ESM (exchange system manager)
if you have numerous servers this will take some time to replicate based on your policy for that.
pwanveerAuthor Commented:
You're a rockstar! That's got it. Thank you.
de nada
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