Find obsolete guest accounts by activity (v3)

# Review required modules and connection steps before running.
# Connect to Microsoft Graph or Exchange Online as needed for this script.

param(
    [int] $LookbackDays = 90,
    [string] $StartDate = "Get-Date(Get-Date).AddDays(-$LookbackDays) #For audit log",
    [string] $EndDate = "Get-Date; $Active = 0; $EmailActive = 0; $AuditRec = 0; $GNo = 0"
)
 
$ModulesLoaded = Get-Module | Select-Object Name
If (!($ModulesLoaded -match "ExchangeOnlineManagement")) {Write-Host "Please connect to the Exchange Online Management module and then restart the script"; break}
If (!($ModulesLoaded -match "Microsoft.Graph.Authentication")) {Write-Host "Please connect to the Microsoft Graph PowerShell SDK and then restart the script"; break}
# OK, we seem to be fully connected
# Start by finding all Guest Accounts
Write-Host "Finding Guest Accounts"
[array]$Guests = (Get-MgUser -Filter "usertype eq 'Guest'" -All `
  -Property  id, UserPrincipalName, displayName, createdDateTime, mail `
  | Sort-Object DisplayName)
If (!($Guests)) {
   Write-Host "No guest accounts can be found - exiting" ; break
}
$StartDate2 = Get-Date(Get-Date).AddDays(-$LookbackDays) #For message trace
$Report = [System.Collections.Generic.List[Object]]::new() # Create output file for report
Clear-Host
Write-Host ("{0} guest accounts found. Checking their activity..." -f $Guests.Count)
ForEach ($G in $Guests) {
   $GNo++
   $ProgressBar = "Processing guest " + $G.DisplayName + " (" + $GNo + " of " + $Guests.Count + ")"
   Write-Progress -Activity "Checking Guest Accounts for activity" -Status $ProgressBar -PercentComplete ($GNo/$Guests.Count*100)
   $LastAuditRecord = $Null; $GroupNames = $Null; $LastAuditAction = $Null; $ReviewFlag = $False
   $GuestId = $G.Id
   # Search for audit records for this user
   [array]$Recs = (Search-UnifiedAuditLog -UserIds $G.Mail, $G.UserPrincipalName -Operations UserLoggedIn, SecureLinkUsed, TeamsSessionStarted -StartDate $StartDate -EndDate $EndDate -ResultSize 1)
   If ($Recs) { # We found some audit records
      $LastAuditRecord = $Recs[0].CreationDate; $LastAuditAction = $Recs[0].Operations; $AuditRec++
   } Else {
      $LastAuditRecord = "None found"; $LastAuditAction = "N/A"
   }
    # Check email tracking logs because guests might receive email through membership of Outlook Groups. Email address must be valid for the check to work
   If ($Null -ne $G.Mail) {
      [array]$EmailRecs = (Get-MessageTrace -StartDate $StartDate2 -EndDate $EndDate -Recipient $G.Mail)
   }
   If ($EmailRecs.Count -gt 0) {
      $EmailActive++
   }
 
   # Find what Microsoft 365 Groups the guest belongs to
   $GroupNames = $Null
   [array]$GuestGroups = Get-MgUserMemberOf -UserId $GuestId -All | `
    Where-Object {$_.AdditionalProperties["groupTypes"] -eq "Unified"} | `
    Select-Object -ExpandProperty AdditionalProperties
    If ($Null -ne $GuestGroups) {
      $GroupNames = $GuestGroups.displayName -join ", "
   }
 
    # Figure out the domain the guest is from so that we can report this information
   $Domain = $G.Mail.Split("@")[1]
   # Figure out age of guest account in days using the creation date in the extension properties of the guest account
   $AccountAge = ($G.CreatedDateTime | New-TimeSpan).Days
   # Find if there's been any recent sign on activity
   $UserLastLogonDate = $Null
   $UserLastLogonDate = (Get-MgAuditLogSignIn -Top 1 -Filter "userid eq '$GuestId'").CreatedDateTime
   If ($Null -ne $UserLastLogonDate) {
      $UserLastLogonDate = Get-Date ($UserLastLogonDate) -format g
   } Else {
      $UserLastLogonDate = "No recent sign in records found"
   }
   # Flag the account for potential deletion if it is more than a year old and isn't a member of any Office 365 Groups.
   If (($AccountAge -gt 365) -and ($Null -eq $GroupNames))  {
      $ReviewFlag = $True
   }
     # Write out report line
   $ReportLine = [PSCustomObject]@{
          Guest                = $G.Mail
          Name                 = $G.DisplayName
          Domain               = $Domain
          Inactive             = $ReviewFlag
          Created              = $G.CreatedDateTime
          AgeInDays            = $AccountAge
          EmailCount           = $EmailRecs.Count
          "Last sign-in"       = $UserLastLogonDate
          "Last Audit record"  = $LastAuditRecord
          "Last Audit action"  = $LastAuditAction
          "Member of"          = $GroupNames
          UPN                  = $G.UserPrincipalName
          ObjectId             = $G.Id }
   $Report.Add($ReportLine)
   # Update guest account in Entra ID with details of review
   $ActiveText = "Active"
   If ($ReviewFlag -eq $True) {
      $ActiveText = "inactive"
   }
   $Text = ("Guest account last reviewed on {0} when account was deemed {1}" -f (Get-Date -format g), $ActiveText)
   Update-MgUser -UserId $G.Id -OnPremisesExtensionAttributes @{'extensionAttribute1' = $Text}
}
# Generate the output files
$Report | Sort-Object Name | Export-CSV -NoTypeInformation c:\temp\GuestActivity.csv
$Report | Where-Object {$_.Inactive -eq $True} | Select-Object ObjectId, Name, UPN, AgeInDays | Export-CSV -NotypeInformation c:\temp\InActiveGuests.CSV
Clear-Host
$Active = $AuditRec + $EmailActive
# Figure out the domains guests come from
$Domains = $Report.Domain | Sort-Object
$DomainsCount = @{}
$Domains | ForEach-Object {$DomainsCount[$_]++}
$DomainsCount = $DomainsCount.GetEnumerator() | Sort-Object -Property Value -Descending
$DomainNames = $Domains | Sort-Object -Unique
 
$PercentInactive = (($Guests.Count - $Active)/$Guests.Count).toString("P")
Write-Host ""
Write-Host "Statistics"
Write-Host "----------"
Write-Host "Guest Accounts           " $Guests.Count
Write-Host "Active Guests            " $Active
Write-Host "Audit Record found       " $AuditRec
Write-Host "Active on Email          " $EmailActive
Write-Host "InActive Guests          " ($Guests.Count - $Active)
Write-Host "Percent inactive guests  " $PercentInactive
Write-Host "Number of guest domains  " $DomainsCount.Count
Write-Host ("Domain with most guests   {0} ({1})" -f $DomainsCount[0].Name, $DomainsCount[0].Value)
Write-Host " "
Write-Host "Guests found from domains " ($DomainNames -join ", ")
Write-Host " "
Write-Host "The output file containing detailed results is in c:\temp\GuestActivity.csv"
Write-Host "A CSV file containing the User Principal Names of inactive guest accounts is in c:\InactiveGuests.csv"