Export Microsoft 365 Mailboxes, Aliases, and Sizes with PowerShell

Overview

If you need a complete picture of your Microsoft 365 mailboxes — primary addresses, aliases, mailbox types, sizes, and item counts — Exchange Online PowerShell gives you everything in one place. This guide walks through connecting to Exchange Online, querying mailbox data, and producing a clean CSV export you can open directly in Excel, Google Sheets, or LibreOffice.

This is the kind of task that comes up regularly in identity audits, mailbox consolidation projects, licence reviews, and migration planning.

Install the Exchange Online Module

Run this once on the machine you will use to connect. If prompted to trust PSGallery, accept.

Install-Module ExchangeOnlineManagement -Scope CurrentUser

Connect to Exchange Online

Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline

A Microsoft login window will open. Sign in with a Global Admin or Exchange Admin account.

Query All Mailboxes

The core mailbox data comes from Get-EXOMailbox. The EmailAddresses property contains all addresses for a mailbox — the primary SMTP address is prefixed with SMTP: (uppercase), and aliases are prefixed with smtp: (lowercase).

Get-EXOMailbox -ResultSize Unlimited |
Select-Object `
    DisplayName,
    UserPrincipalName,
    PrimarySmtpAddress,
    RecipientTypeDetails,
    EmailAddresses

Field	Meaning
DisplayName	Mailbox display name
UserPrincipalName	Login email / UPN
PrimarySmtpAddress	Primary mailbox address
RecipientTypeDetails	Mailbox type
EmailAddresses	All addresses including aliases

Mailbox Types You Will Encounter

Type	Meaning
UserMailbox	Standard user mailbox
SharedMailbox	Shared mailbox
RoomMailbox	Meeting room resource
EquipmentMailbox	Equipment resource
DiscoveryMailbox	Compliance and eDiscovery mailbox

Add Mailbox Size

Mailbox size is not part of Get-EXOMailbox — it comes from Get-EXOMailboxStatistics. You need to combine both calls. The example below converts the size to GB for a clean numeric output.

$mailboxes = Get-EXOMailbox -ResultSize Unlimited

$result = foreach ($m in $mailboxes) {

    $stats = Get-EXOMailboxStatistics -Identity $m.UserPrincipalName

    $sizeBytes = $stats.TotalItemSize.Value.ToBytes()
    $sizeGB    = [math]::Round($sizeBytes / 1GB, 2)

    $aliases = $m.EmailAddresses |
        Where-Object { $_ -like "smtp:*" } |
        ForEach-Object { $_.Replace("smtp:", "") }

    [PSCustomObject]@{
        DisplayName       = $m.DisplayName
        UserPrincipalName = $m.UserPrincipalName
        PrimaryEmail      = $m.PrimarySmtpAddress
        MailboxType       = $m.RecipientTypeDetails
        MailboxSizeGB     = $sizeGB
        ItemCount         = $stats.ItemCount
        Aliases           = ($aliases -join ";")
    }
}

Export to CSV

CSV is the most practical format for reviewing mailbox data. It opens directly in Excel, Google Sheets, or LibreOffice with no additional processing.

$result | Export-Csv "mailboxes.csv" -NoTypeInformation

Example output:

DisplayName	UserPrincipalName	PrimaryEmail	MailboxType	MailboxSizeGB	ItemCount	Aliases
John Smith	`john@company.com`	`john@company.com`	UserMailbox	2.45	18420	`john.smith@company.com;j.smith@company.com`
Support	`support@company.com`	`support@company.com`	SharedMailbox	12.31	92011	`help@company.com`

Export to JSON

Use JSON if you need to feed the output into another system or script.

$result | ConvertTo-Json -Depth 3 | Out-File "mailboxes.json"

Include Licence Status (Optional)

Licence data is not available through Exchange Online — it requires Microsoft Graph. Install the module once:

Install-Module Microsoft.Graph -Scope CurrentUser

Connect with the required scopes:

Connect-MgGraph -Scopes "User.Read.All","Directory.Read.All"

Query assigned licences:

Get-MgUser -All |
Select-Object DisplayName, UserPrincipalName, AssignedLicenses

If you need licence status combined with mailbox data in the same export, that can be scripted by joining on UserPrincipalName.

Disconnect When Finished

Disconnect-ExchangeOnline

Full Script

Here is everything combined into a single script that produces a clean CSV.

Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline

$mailboxes = Get-EXOMailbox -ResultSize Unlimited

$result = foreach ($m in $mailboxes) {

    $stats = Get-EXOMailboxStatistics -Identity $m.UserPrincipalName

    $sizeBytes = $stats.TotalItemSize.Value.ToBytes()
    $sizeGB    = [math]::Round($sizeBytes / 1GB, 2)

    $aliases = $m.EmailAddresses |
        Where-Object { $_ -like "smtp:*" } |
        ForEach-Object { $_.Replace("smtp:", "") }

    [PSCustomObject]@{
        DisplayName       = $m.DisplayName
        UserPrincipalName = $m.UserPrincipalName
        PrimaryEmail      = $m.PrimarySmtpAddress
        MailboxType       = $m.RecipientTypeDetails
        MailboxSizeGB     = $sizeGB
        ItemCount         = $stats.ItemCount
        Aliases           = ($aliases -join ";")
    }
}

$result | Export-Csv "mailboxes.csv" -NoTypeInformation

Disconnect-ExchangeOnline

The output CSV gives you a full mailbox audit: who owns the mailbox, what type it is, its primary address, all aliases, current storage consumption, and total item count. That is a solid starting point for any identity audit, migration assessment, or licence review.