<#
=============================================================================================
Name:           Audit Senas emails
Description:    This script monitors emails that sent using SendAs permission
Version:        1.0
Website:        o365reports.com

Script Highlights: 
~~~~~~~~~~~~~~~~~~

1.The script uses modern authentication to retrieve audit logs.  
2.The script can be executed with MFA enabled account too.    
3.Exports report results to CSV file.    
4.Helps to find out who sent email from a shared mailbox.  
5.Allows you to generate send as email audit report for a custom period.    
6.Automatically installs the EXO V2 module (if not installed already) upon your confirmation.   
7.The script is scheduler-friendly. i.e., Credential can be passed as a parameter instead of saving inside the script. 

For detailed script execution: https://o365reports.com/2022/03/30/audit-send-as-emails-in-microsoft-365-using-powershell
============================================================================================
#>
Param
(
    [Parameter(Mandatory = $false)]
    [Nullable[DateTime]]$StartDate,
    [Nullable[DateTime]]$EndDate,
    [string]$UserName,
    [string]$Password
)

Function Connect_Exo
{
 #Check for EXO v2 module inatallation
 $Module = Get-Module ExchangeOnlineManagement -ListAvailable
 if($Module.count -eq 0) 
 { 
  Write-Host Exchange Online PowerShell V2 module is not available  -ForegroundColor yellow  
  $Confirm= Read-Host Are you sure you want to install module? [Y] Yes [N] No 
  if($Confirm -match "[yY]") 
  { 
   Write-host "Installing Exchange Online PowerShell module"
   Install-Module ExchangeOnlineManagement -Repository PSGallery -AllowClobber -Force
   Import-Module ExchangeOnlineManagement
  } 
  else 
  { 
   Write-Host EXO V2 module is required to connect Exchange Online.Please install module using Install-Module ExchangeOnlineManagement cmdlet. 
   Exit
  }
 } 
 Write-Host Connecting to Exchange Online...
 #Storing credential in script for scheduling purpose/ Passing credential as parameter - Authentication using non-MFA account
 if(($UserName -ne "") -and ($Password -ne ""))
 {
  $SecuredPassword = ConvertTo-SecureString -AsPlainText $Password -Force
  $Credential  = New-Object System.Management.Automation.PSCredential $UserName,$SecuredPassword
  Connect-ExchangeOnline -Credential $Credential
 }
 else
 {
  Connect-ExchangeOnline
 }
}

$MaxStartDate=((Get-Date).AddDays(-89)).Date

#Getting SendAs emails for past 90 days
if(($StartDate -eq $null) -and ($EndDate -eq $null))
{
 $EndDate=(Get-Date).Date
 $StartDate=$MaxStartDate
}
#Getting start date to audit sendas emails report
While($true)
{
 if ($StartDate -eq $null)
 {
  $StartDate=Read-Host Enter start time for report generation '(Eg:04/28/2021)'
 }
 Try
 {
  $Date=[DateTime]$StartDate
  if($Date -ge $MaxStartDate)
  { 
   break
  }
  else
  {
   Write-Host `nAudit can be retrieved only for past 90 days. Please select a date after $MaxStartDate -ForegroundColor Red
   return
  }
 }
 Catch
 {
  Write-Host `nNot a valid date -ForegroundColor Red
 }
}


#Getting end date to audit sendas emails report
While($true)
{
 if ($EndDate -eq $null)
 {
  $EndDate=Read-Host Enter End time for report generation '(Eg: 04/28/2021)'
 }
 Try
 {
  $Date=[DateTime]$EndDate
  if($EndDate -lt ($StartDate))
  {
   Write-Host End time should be later than start time -ForegroundColor Red
   return
  }
  break
 }
 Catch
 {
  Write-Host `nNot a valid date -ForegroundColor Red
 }
}

$OutputCSV=".\AuditSendAsEmailsReport_$((Get-Date -format yyyy-MMM-dd-ddd` hh-mm` tt).ToString()).csv" 
$IntervalTimeInMinutes=1440    #$IntervalTimeInMinutes=Read-Host Enter interval time period '(in minutes)'
$CurrentStart=$StartDate
$CurrentEnd=$CurrentStart.AddMinutes($IntervalTimeInMinutes)

#Check whether CurrentEnd exceeds EndDate
if($CurrentEnd -gt $EndDate)
{
 $CurrentEnd=$EndDate
}

if($CurrentStart -eq $CurrentEnd)
{
 Write-Host Start and end time are same.Please enter different time range -ForegroundColor Red
 Exit
}

Connect_EXO
$CurrentResultCount=0
$AggregateResultCount=0
Write-Host `nAuditing sendas emails from $StartDate to $EndDate...
$ProcessedAuditCount=0
$OutputEvents=0
$ExportResult=""   
$ExportResults=@()  


while($true)
{
 #Getting audit data for the given time range
 Search-UnifiedAuditLog -StartDate $CurrentStart -EndDate $CurrentEnd -Operations SendAs -SessionId s -SessionCommand ReturnLargeSet -ResultSize 5000 | ForEach-Object {
  $ResultCount++
  $ProcessedAuditCount++
  Write-Progress -Activity "`n     Retrieving sendas activities from $CurrentStart to $CurrentEnd.."`n" Processed audit record count: $ProcessedAuditCount"
  $MoreInfo=$_.auditdata
  $Operation=$_.Operations
  $SentBy=$_.UserIds
  if($SentBy -eq "S-1-5-18")
  {
   $SentBy="Service account"
  }
  $AuditData=$_.auditdata | ConvertFrom-Json
  $SentAs=$AuditData.SendAsUserSMTP
  $Subject=$AuditData.Item.Subject
  $Result=$AuditData.ResultStatus
  $PrintFlag="True"
  $SentTime=(Get-Date($AuditData.CreationTime)).ToLocalTime()  #Get-Date($AuditData.CreationTime) Uncomment to view the Activity Time in UTC
   #Export result to csv
   $OutputEvents++
     #Export result to csv
  $ExportResult=@{'Sent Time'=$SentTime;'Sent By'=$SentBy;'Sent As'=$SentAs; 'Subject'=$Subject; 'Operation'=$Operation;'Result'=$Result;'More Info'=$MoreInfo}
  $ExportResults= New-Object PSObject -Property $ExportResult  
  $ExportResults | Select-Object 'Sent Time','Sent By','Sent As','Subject','Operation','Result','More Info' | Export-Csv -Path $OutputCSV -Notype -Append 
  
 }
 $currentResultCount=$currentResultCount+$ResultCount
 
 if($CurrentResultCount -ge 50000)
 {
  Write-Host Retrieved max record for current range.Proceeding further may cause data loss or rerun the script with reduced time interval. -ForegroundColor Red
  $Confirm=Read-Host `nAre you sure you want to continue? [Y] Yes [N] No
  if($Confirm -match "[Y]")
  {
   Write-Host Proceeding audit log collection with data loss
   [DateTime]$CurrentStart=$CurrentEnd
   [DateTime]$CurrentEnd=$CurrentStart.AddMinutes($IntervalTimeInMinutes)
   $CurrentResultCount=0
   if($CurrentEnd -gt $EndDate)
   {
    $CurrentEnd=$EndDate
   }
  }
  else
  {
   Write-Host Please rerun the script with reduced time interval -ForegroundColor Red
   Exit
  }
 }

 
 if($ResultCount -lt 5000)
 { 
  if($CurrentEnd -eq $EndDate)
  {
   break
  }
  $CurrentStart=$CurrentEnd 
  if($CurrentStart -gt (Get-Date))
  {
   break
  }
  $CurrentEnd=$CurrentStart.AddMinutes($IntervalTimeInMinutes)
  $CurrentResultCount=0
  if($CurrentEnd -gt $EndDate)
  {
   $CurrentEnd=$EndDate
  }
 }                                                                                             
 $ResultCount=0
}

#Open output file after execution
If($OutputEvents -eq 0)
{
 Write-Host No records found
}
else
{
 Write-Host `nThe output file contains $OutputEvents audit records `n
 if((Test-Path -Path $OutputCSV) -eq "True") 
 {
  Write-Host " The Output file availble in:" -NoNewline -ForegroundColor Yellow
  Write-Host  $OutputCSV 
  $Prompt = New-Object -ComObject wscript.shell   
  $UserInput = $Prompt.popup("Do you want to open output file?",`   
 0,"Open Output File",4)   
  If ($UserInput -eq 6)   
  {   
   Invoke-Item "$OutputCSV"  
  } 
 }
}

#Disconnect Exchange Online session
Disconnect-ExchangeOnline -Confirm:$false -InformationAction Ignore -ErrorAction SilentlyContinue
  Write-Host `n~~ Script prepared by AdminDroid Community ~~`n -ForegroundColor Green 
  Write-Host "~~ Check out " -NoNewline -ForegroundColor Green; Write-Host "admindroid.com" -ForegroundColor Yellow -NoNewline; Write-Host " to get access to 1800+ Microsoft 365 reports. ~~" -ForegroundColor Green `n`n