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Single Sign-On With Multiple Email Addresses Per User

  • How can I add an additional email address to a single sign-on user? When I try using the Web Interface I get a message like this:


    The operation on mailbox "User Name" failed because it's out of the current user's write scope. The action 'Set-Mailbox', 'EmailAddresses', can't be performed on the object 'User Name' because the object is being synchronized from your on-premises organization. This action should be performed on the object in your on-premises organization.


    I can't add email addresses locally because we don't run Exchange. I believe this uses the AD Proxy field but as our schema doesn't have that field I can't edit it. 

    Can anyone help?

  • Hello Mark,

    Your e-mail addresses are contained in the ProxyAddresses AD attribute, which should be part of your default AD implementation.  And as always, you can extend your schema using the Exchange 2010 trial disc, as you don't actually have to install Exchange in order to extend the schema and add all of the Exchange attributes.  Modify that attribute in your local AD and it'll add those addresses to the Office 365 object during the next sync.

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  • How?

  • In "Active Directory Users and Computers", switch to advanced view (View | Advanced Features) and you will see the "Attribute Editor" tab in the user's properties. There you can edit the ProxyAddresses field.

    To add email addresses, add the prefix "SMTP:" (for the main account) and "smtp:" for aliases. More details here:


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  • 1. In Active Directory Users and Computers, enable advanced view: View | Advanced Features.

    2. In the user’s properties, go to tab Attribute Editor.

    3. Add the email addresses in to the proxyAddresses attribute, with the prefix "SMTP:" for the main account, and "smpt:" for aliases.

    More info:


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  • Thank you.