Who owns an email alias in Office365?

How do you find if an email address is assigned to a user in Office365?

A quick an easy way today - how do you find out if an email address/alias is assigned to a user in your Office365 tenancy?

It's pretty easy really - although not that obvious.

For both of these methods, you'll need to connect to Office365 with PowerShell. To do that, you need to do the following:


At this point, you'll be prompted to enter your Office365 Admin Credentials

Then, you connect to the session using those credentials (below may be wrapped - the $session and Import-PSSession are two lines).

$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $Cred -Authentication Basic -AllowRedirection
Import-PSSession $Session

You could then if you wanted export all of your mailbox identities with their email addresses. You can do that with:

get-mailbox -identity *|select-object Identity, EmailAddresses|export-csv

This would put all of your mailboxes and associated Email-Addresses into a CSV.

More specifically, you could just search for the email address you're interested in - you can do that with this command:

Get-Mailbox -Identity * | Where-Object {$_.EmailAddresses -like 'smtp:
emailaddress@domain.com'} | Format-List Identity, EmailAddresses

Obviously change the 'emailaddress@domain.com' to whatever you're looking for. You can use wildcards too, so for example DA*@contoso.com would find any alias beginning with DA and @contoso.com

Output is similar to this:


In the words of Heath Ledger…Da Daaaaaa.

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