PowerShell: check to see if Office365 email addresses exist

not a Unix thing, but I use this to see what Office365 email addresses that are valid as they traverse Unix email systems.

# References::
# https://msdn.microsoft.com/en-us/library/azure/Dn194133.aspx
# https://technet.microsoft.com/en-us/library/JJ984289%28v=EXCHG.150%29.aspx
# https://gallery.technet.microsoft.com/office/Office-365-Search-Users-ff560fb8

# First we see if we haven't already logged in - if not, then ask the user
if ( !$Office365Credentials  ) {
    #Remove all existing Powershell sessions 
    Get-PSSession | Remove-PSSession 

    # Get creds from the user with a popup... eg. firstname.lastname@somedept.gov + PaSsWoRd
    $Office365Credentials = Get-Credential
     
    #Create remote Powershell session 
    $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $Office365credentials -Authentication Basic -AllowRedirection
        
    #Import the session 
    Import-PSSession $Session -AllowClobber

    # Connect to MS online with the same credentials
    Connect-MsolService -Credential $Office365Credentials

    # Cache the entries for Users and Groups
    Write-Host "caching users and groups"
    $Users = Get-MsolUser -All | Select UserPrincipalName,ProxyAddresses
    $Groups = Get-MsolGroup -SearchString $SearchForThis | Select EmailAddress,ProxyAddresses
}

$SearchForThis = Read-Host -Prompt 'Input your search string::'

Write-Host "Checking for Users UserPrincipalName,ProxyAddresses matching $SearchForThis" -ForegroundColor Yellow

ForEach ($User in $Users) {

    if ($User.UserPrincipalName -eq $SearchForThis) {
        Write-Host "Found Exact Match UserPrincipalName:" $User.UserPrincipalName -ForegroundColor Green
    } ElseIf ($User.UserPrincipalName -Match $SearchForThis) {
        Write-Host "Found UserPrincipalName:" $User.UserPrincipalName -ForegroundColor Green
    }
         
    ForEach ($ProxyAddress in $User.ProxyAddresses) {
        #Write-Host $ProxyAddress -ForegroundColor Red
   
        If ($ProxyAddress -eq $SearchForThis) { 
            Write-Host "Found Exact Match ProxyAddress for" $User.UserPrincipalName $ProxyAddress -ForegroundColor Magenta
        } elseif ($ProxyAddress –Match $SearchForThis) { 
            Write-Host "Found ProxyAddress for" $User.UserPrincipalName $ProxyAddress -ForegroundColor Magenta
        } 
    }

} 


Write-Host "Checking Groups for EmailAddress,ProxyAddresses matching $SearchForThis" -ForegroundColor Yellow

ForEach ($Group in $Groups) {

    if ($Group.EmailAddress -eq $SearchForThis) {
        Write-Host "Found Exact Match EmailAddress:" $Group.EmailAddress -ForegroundColor Green
    } ElseIf ($Group.EmailAddress -Match $SearchForThis) {
        Write-Host "Found EmailAddress:" $Group.EmailAddress -ForegroundColor Green
    }

    ForEach ($ProxyAddress in $Group.ProxyAddresses) {
        If ($ProxyAddress -eq $SearchForThis) { 
            Write-Host "Found Exact Match EmailAddress for" $Group.EmailAddress $ProxyAddress -ForegroundColor Magenta
        } ElseIf ($ProxyAddress –Match $SearchForThis) { 
            Write-Host "Found ProxyAddress for" $Group.EmailAddress $ProxyAddress -ForegroundColor Magenta
        } 
    }

} 
# if this is a stand alone script, we drop teh session
#Remove-PSSession $Session