How to get all users with alias as subdomain

Question

Hello All,

We need to pull a report where users having alias as our subdomains

We have around 20k users and we need to filter out them with our subdomains (15).

Please suggest a quick and easy to figure it out, pulling out the entire report and checking is consuming lot of time.

Example: Mani is having primary smtp with microsoft and alias with onmicrosoft, contoso

And i need to pull report for contoso from all 20k users.

Answer 1

Hello, @Mani,

Welcome to the Microsoft Q&A platform!

To efficiently pull a report of users with specific subdomain aliases, you can use PowerShell. Here's a script that can help you filter out users with the "contoso" subdomain from your 20k users:

1.Open PowerShell with administrative privileges.

2.Run the following script:

# Connect to Exchange Online
Connect-ExchangeOnline -UserPrincipalName ******@domain.com -ShowProgress $true

# Define the subdomain to filter
$subdomain = "contoso"

# Get all users and filter by alias
$users = Get-Mailbox -ResultSize Unlimited | Where-Object {
    $_.EmailAddresses -match $subdomain
}

# Export the filtered users to a CSV file
$users | Select-Object DisplayName, PrimarySmtpAddress, EmailAddresses | Export-Csv -Path "C:\Users\YourUsername\Documents\FilteredUsers.csv" -NoTypeInformation

# Disconnect from Exchange Online
Disconnect-ExchangeOnline -Confirm:$false

Test Results:

This script should help you quickly generate the report you need without manually checking each user. Let me know if you need any further assistance!

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If the answer is helpful, please click on “Accept answer” as it could help other members of the Microsoft Q&A community who have similar questions and are looking for solutions.

Thank you for your support and understanding.

Best Wishes,

Alex Zhang

Answer 2

You can use server-side filtering for that. For example, to list all recipients associated with the .onmicrosoft.com domain, you can do this:

Get-Recipient -RecipientPreviewFilter {EmailAddresses -like "*@tenant.onmicrosoft.com"}

If you only care about mailboxes, use Get-Mailbox with the -Filter parameter instead.