These are great questions. I'll deal with them individually.
First of all, I believe you're asking how to set up the SMTP address of your e-mail accounts to be @abc.com.
There are multiple parts to this question. Setting the SMTP domain to be @abc.com is pretty simple. Essentially, you need to launch Exchange System Manager, navigate to Recipient Policies -> Default Policy -> Properties -> E-mail Addresses and set SMTP Address to @abc.com. All new mailboxes created henceforth will have an e-mail address in the format firstname.lastname@example.org.
If you have to change the SMTP addresses of mailboxes that you have already created (i.e., if you have a lot of existing mailboxes already created), you'll have to resort to either changing them manually through Active Directory Users and Computers, or using the Ldifde tool to export all mailboxes, modify the SMTP address and re-import into Active Directory. (See Microsoft Knowledge Base article 313823.)
Secondly, supporting a second SMTP domain is as simple as setting some sort of unique identifier on all accounts that will sport the --> --> --> --> .com SMTP address and then specifying a second recipient policy based on this criteria. Depending on the business drivers behind your particular requirements, you may decide to put all @123.com users in a given Organizational Unit (OU) in Active Directory, or you may wish to include specific text in one attribute on all these accounts -- for example, Custom Attribute = "123 Company" or similar. Then you'll want to create the recipient policy for @123.com. You'll need to specify an LDAP query for the second recipient policy that only returns the mailboxes that you've created. Once again, you'll need to the Recipient Policies node, then select the new Recipient Policy that you've created for 123 Company, navigate to Properties -> E-mail Addresses, and set the SMTP Address to @123.com.
One final reminder: Any SMTP domains that you set up are only as good as the DNS MX records that you have defined with your Internet Service Provider and Internet Domain Registrar. Obviously, you need a proper MX record set up for both @abc.com and @123.com pointing to your SMTP gateway if your Exchange server is going to actually receive any Internet traffic destined for these domains!
MEMBER FEEDBACK TO THIS ASK THE EXPERT Q&A:
ADmodify.exe is a great tool for mass modifying of Active Directory users' e-mail addresses. You can add mail domains based on current user e-mail name or AD first.last, etc. It's easier than doing LDIFDE.
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This was first published in February 2005