Get-MailBoxSizesOU.ps1

################################################################################################################################################################
# To run the script
#
# .\Get-MailBoxSizesOU.ps1
#
# NOTE: If you do not pass an input file to the script, it will return the sizes of ALL mailboxes in the tenant.  Not advisable for tenants with large
# user count (< 3,000)
#
#Supports Modern Authentication and Multi Factor Authenication
#Dependenices: Exchange Online Module
#
# Author: 				Terry Wensel
# Version: 				1.0
# Last Modified Date: 	7/5/2018
# Last Modified By: 	Terry Wensel
################################################################################################################################################################

#Constant Variables
$OutputFile = "C:\temp\MailboxSizes.csv"   #The CSV Output file that is created, change for your purposes
$SearchBase = 'OU=Users,OU=United Kingdom,OU=Locations,DC=eriezusa,DC=net'
#Main
Function Main {
	#Remove all existing Powershell sessions
	Get-PSSession | Remove-PSSession
	#Call ConnectTo-ExchangeOnline function with correct credentials
	ConnectTo-ExchangeOnline
	#Prepare Output file with headers
	Out-File -FilePath $OutputFile -InputObject "UserPrincipalName,NumberOfItems,MailboxSize" -Encoding UTF8
	
    #No input file found, gather all mailboxes from Office 365 where the accounts are in a specific OU
	$objUsers = Get-ADUser -Filter * -SearchBase $SearchBase | select-object UserPrincipalName
	
	#Iterate through all users
	Foreach ($objUser in $objUsers)
	{
		#Connect to the users mailbox
		$objUserMailbox = get-mailboxstatistics -Identity $($objUser.UserPrincipalName) | Select ItemCount,TotalItemSize
		#Prepare UserPrincipalName variable
		$strUserPrincipalName = $objUser.UserPrincipalName
		#Get the size and item count
		$ItemSizeString = $objUserMailbox.TotalItemSize.ToString()
		$strMailboxSize = "{0:N2}" -f ($ItemSizeString.SubString(($ItemSizeString.IndexOf("(") + 1),($itemSizeString.IndexOf(" bytes") - ($ItemSizeString.IndexOf("(") + 1))).Replace(",","")/1024/1024)
		$strItemCount = $objUserMailbox.ItemCount
		#Output result to screen for debuging (Uncomment to use)
		#write-host "$strUserPrincipalName : $strLastLogonTime"
		#Prepare the user details in CSV format for writing to file
	  $strUserDetails = "$strUserPrincipalName,$strItemCount,$strMailboxSize"
		#Append the data to file
		Out-File -FilePath $OutputFile -InputObject $strUserDetails -Encoding UTF8 -append
	}
	#Clean up session
	Get-PSSession | Remove-PSSession
}
###############################################################################
#
# Function ConnectTo-ExchangeOnline
#
# PURPOSE
#    Connects to Exchange Online Remote PowerShell using the tenant credentials
#
# RETURN
#    None.
#
###############################################################################
function ConnectTo-ExchangeOnline
{
	#Create remote Powershell session

    $modules = @(Get-ChildItem -Path "$($env:LOCALAPPDATA)\Apps\2.0" -Filter "Microsoft.Exchange.Management.ExoPowershellModule.manifest" -Recurse )
    $moduleName =  Join-Path $modules[0].Directory.FullName "Microsoft.Exchange.Management.ExoPowershellModule.dll"
    Import-Module -FullyQualifiedName $moduleName -Force
    $scriptName =  Join-Path $modules[0].Directory.FullName "CreateExoPSSession.ps1"
    . $scriptName
    $null = Connect-EXOPSSession
    $session = (Get-PSSession | Where-Object { ($_.ConfigurationName -eq 'Microsoft.Exchange') -and ($_.State -eq 'Opened') })[0]

    #Import the session
    Import-PSSession $Session -AllowClobber | Out-Null
}
# Start script
. Main