O365 – Determine Mailbox Folder Size from Exchange Online using PowerShell

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I’m sure all Exchange Online environments have users who are data hoarders in their email environment. Most tenants have policies to limit how big the mailbox can be for various reasons. Users may come back with increasing mailbox sizes so they can hoard more of those outdated data. It is good practice to maintain the folder items. Get-MailboxFolderStatistics helps retrieve information about folders in mailboxes, including number and size of items in the folder and other information.

Before proceeding, make sure you are connected to Exchange Online module,

$credential = Get-Credential
Connect-ExchangeOnline -credential $credential

To determine a folders from a user’s mailbox, the folder size and the number of items in the folders,

$EmailId = Read-Host "Enter user's email address"
Get-MailboxFolderStatistics -Identity $EmailId | Select Name,FolderSize,ItemsinFolder

To determine individual folders and subfolder sizes of a specific user:

$EmailId = Read-Host "Enter user's email address"
Get-MailboxFolderStatistics -Identity $EmailId | Select Name,FolderAndSubfolderSize,ItemsInFolderAndSubfolders

To determine inbox folders statistics of a specific user:

$EmailId = Read-Host "Enter user's email address"
Get-MailboxFolderStatistics -Identity $EmailId -FolderScope Inbox | Format-Table Identity,ItemsInFolderAndSubfolders,FolderAndSubfolderSize -AutoSize

To determine and display inbox folder sizes for all mailboxes in the organization 

$All = Get-Mailbox -ResultSize Unlimited
$All | foreach {Get-MailboxFolderStatistics -Identity $_.Identity -FolderScope Inbox} | Select Identity,ItemsInFolderAndSubfolders,FolderAndSubfolderSize | ft -AutoSize

and export to CSV file:

$Allmbx = Get-Mailbox -ResultSize Unlimited
$Allmbx | foreach {Get-MailboxFolderStatistics -Identity $_.Identity -FolderScope Inbox | Select Identity,ItemsInFolderAndSubfolders,FolderAndSubfolderSize | Export-Csv "C:\tmp\Inbox_data.csv" -NoTypeInformation -Append}

Get-MailboxFolderStatistics returns IPM subtree folders. This folder structure consists of messages between recipients(Inbox, Sent Items). In the Exchange Online, the Non-IMP subtree is quite larger, as different O365 applications have been using mailboxes to store and process data. Teams, Delve, MyAnalytics, all have their own folders or folder trees inside the Non-IPM root.

To determine Non-IPM subtree folders and their sizes:

$EmailId = Read-Host "Enter user's email address"
Get-MailboxFolderStatistics -Identity $EmailId -FolderScope NonIpmRoot | Format-Table Identity,ItemsInFolderAndSubfolders,FolderAndSubfolderSize -AutoSize

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