Update multiple Primary SMTP address in ProxyAddress attribute in AD

Someone has somehow removed the Primary SMTP addresses in AD, we'll figure out how late, but is there a way to bulk import primary smtp addressses back into proxyaddress atrribute, using a CSV ? Once done we need to sync to O365 as its sending from .onmicrosoft.com mail address currently. Powershell seems like the best solution i guess ??? AD is 2003.

Any help appreciated.
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
PrimarySMTP and ProxyAddress are Exchange AD attributes, so which Exchange is this? On-premise or cloud?
paologiorgioAuthor Commented:
The addresses are set in AD on-Premise and sync to Cloud. They do not have exchange anymore.
Vasil Michev (MVP)Commented:
You can actually do this directly in the cloud via

Set-Mailbox user@domain.com -WindowsEmailAddress new@domain.com

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This will add new@domain.com as the primary SMTP and will keep the previous one as secondary. As for the AD, you can certainly do it via PowerShell, or use tools such as ADModify (.NET edition is the latest): http://www.msexchange.org/articles-tutorials/exchange-server-2003/tools/ADModify-Change-Exchange-Specific-AD-User-Attributes.html

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