This article was previously published under Q291086
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This article outlines the steps to change the default SMTP address space so that Microsoft Exchange Server mailboxes receive mail addressed to the new SMTP address but also receive mail addressed to their old domains as a secondary SMTP address.
For example, the same Exchange Server mailbox can receive mail addressed as email@example.com as well as reply to old messages for firstname.lastname@example.org.
Before you proceed with the Exchange Server configuration, add a new MX record to reflect the new domain name. This new MX record should be added in the Domain Name Service (DNS) provider, which might be part of the Internet Service Provider (ISP).
For additional information and the syntax of the MX record, please see thefollowing article in the Microsoft Knowledge Base:
The correct addition of this MX record can be verified by performing a NameService Lookup, using the new domain name.
You may also want to familiarize yourself with performing directory exports. For additional information about performing directory exports, click the article number below to view the article in the Microsoft Knowledge Base:
Before you manipulate the User.csv file, make a copy. Open the User.csv file in Excel and in the E-mail addresses field locate SMTP: userA@domain1.com. Move this portion of the E-mail addresses field to the Secondary-Proxy-Addresses field. Repeat these steps for all mailboxes.
Remove the E-mail Addresses column, so that there are only Obj-Class, Directory Name, and Secondary-Proxy-Addresses columns.
Save the CSV file. You are prompted to either keep the format or change the format. If you want to keep the format, click Yes.
Import the User.csv file into your Exchange Server Directory.
This should add the secondary-proxy-address to all your users, which was your oldcompany.com address so that old mail will not cause a Non-delivery Report. The primary SMTP was changed in step 4, so the "reply-to" address from now on will be for the newcompany.com.
Open the properties for the Internet Mail Service from the Exchange Server Administrator program. On the Routing tab, if the Internet Mail Service is configured to reroute SMTP, verify that newdomain.com and olddomain.com are listed. If they missing, click Add, and specify incoming for the missing domain.