Get-MailboxStatistics – How to Get Mailbox Size

Get-MailboxStatistics to view mailbox item size and item count.

To retrieve the size or item count of mailboxes, you must use the Get-MailboxStatistics or, even better, the improved Get-EXOMailboxStatistics PowerShell CmdLet.

Both PowerShell commands are part of the Exchange PowerShell module, ‘ExchangeOnlineManagement,’ which you can install using the following command:

Install-Module ExchangeOnlineManagement

After the Exchange management module is installed, you can start retrieving the size and item count of mailboxes.

By far, the best option is to use the new Get-EXOMailboxStatistics as it offers two obvious benefits:

  1. First, it only retrieves essential mailbox statistics (improved performance).
  2. Second, it can easily convert the size value to Bytes, KBs, MBs, and GBs.

The following output shows some basic usage of the Get-EXOMailboxStatistics command:

PS C:\> Get-EXOMailboxStatistics

DisplayName          : Hans Christian Ørsted
MailboxGuid          : b960c39b-1e76-4332-816b-5925f269da37
DeletedItemCount     : 19
ItemCount            : 241
TotalDeletedItemSize : 96.8 KB (99,121 bytes)
TotalItemSize        : 64.29 MB (67,411,850 bytes)

PS C:\> (Get-EXOMailboxStatistics
64.29 MB (67,411,850 bytes)

PS C:\> (Get-EXOMailboxStatistics

PS C:\> (Get-EXOMailboxStatistics

As you notice in the last line, there are no digits provided. So, if you want to list mailbox sizes in GB with a number of digits, you’ll have to do some tweaking.

The following example grabs the TotalItemSize in bytes and converts it to GB with three digits:

PS C:\> [math]::Round((Get-EXOMailboxStatistics[math]::Pow(1024, 3), 3)

Get the Mailbox Size of a Single User

By far, the easiest way to retrieve the mailbox usage of a single user is by using Easy365Manager.

Easy365Manager is a snap-in to Active Directory Users & Computers that consolidate AD and Office 365 management.

Easy365Manager provides two extra tabs (‘Office 365’ and ‘Mailbox’) in user properties that allows you to view and manage your Office 365 mailbox:

Easy365Manager saves you the trouble of constantly logging in to the many ever-changing web consoles provided by Microsoft.

It also lets you perform changes that normally require PowerShell scripting, like calendar delegation or Azure AD Connect synchronization.

Finally, with Easy365Manager, you can safely remove your on-premises Exchange Server, which instantly eliminates a significant burden (and potential risk) from your network.

Download the fully functional 30-day trial here.

You can install Easy365Manager to any PC or server running AD Users & Computers.

Easy365Manager makes no changes to your infrastructure and only takes a few minutes to install and configure.

Get the Mailbox Sizes of Multiple Users

To retrieve the mailbox sizes of multiple users, you should use the Get-EXOMailboxStatistics command.

As mentioned, it performs better than Get-MailboxStatistics and easily converts mailbox sizes to any format you want.

However, I suggest that you always export the size value as bytes. It’s the ‘purest’ value, and you can always convert it in Excel to your desired format.

(if you prefer to output the result in MB or GB, use the conversion method listed previously).

$Mbxs = Get-EXOMailbox -ResultSize Unlimited
$j = $Mbxs.Count
$Result = @()
For ($i = 0; $i -lt $j; $i++){
    $Stats = $Mbxs[$i] | Get-EXOMailboxStatistics
    $MbxInfo = [PSCustomObject] @{
        UPN                     = $Mbx.UserPrincipalName
        DisplayName             = $Stats.DisplayName
        TotalItemSize           = $Stats.totalitemsize.value.ToBytes()
        ItemCount               = $Stats.ItemCount
        TotalDeletedItemSize    = $Stats.TotalDeletedItemSize.value.ToBytes()
    $Pct = [int]($i / $j * 100)
    Write-Progress -Activity "Retrieving stats." -Status "$Pct% Complete:" -PercentComplete ($Pct)
    $Result += $MbxInfo
$Result | ft UPN,DisplayName,TotalItemSize,ItemCount,TotalDeletedItemSize -AutoSize

As the result is stored in a PowerShell object ($Result), you can easily export the result to a CSV file or use it for further automation:

PS C:\> $Result | Export-Csv c:\Temp\MailStats.csv -NoTypeInformation
PS C:\> $Result | % {Write-Host Mailbox of $_.DisplayName has $_.ItemCount items.}
Mailbox of App Mailbox has 2578 items.
Mailbox of Customer Support has 241 items.
Mailbox of Hans Christian Ørsted has 9634 items.