Fix proxy email addresses

Connect-ExchangeOnline -ShowBanner:$false

[array]$Modules = Get-Module -ListAvailable | Where-Object { $_.Name -eq "ExchangeOnlineManagement" }
If (!$Modules) {
    Write-Host "Connecting to Exchange Online..."
    Connect-ExchangeOnline -ShowBanner:$false
}
 
[array]$Domains = Get-AcceptedDomain
$PrimaryDomain = $Domains | Where-Object { $_.Default -eq $true } | Select-Object -ExpandProperty DomainName
[array]$Domains = $Domains | Select-Object -ExpandProperty DomainName
 
Write-Host "Checking mailboxes..."
[array]$Mailboxes = Get-ExoMailbox -ResultSize Unlimited -RecipientTypeDetails UserMailbox, SharedMailbox, RoomMailbox, EquipmentMailbox, discoveryMailbox
$Report = [System.Collections.Generic.List[Object]]::new()
 
ForEach ($Mailbox in $Mailboxes) {
    $ExternalAddresses = $Mailbox.EmailAddresses | Where-Object { $_ -like "SMTP:*" -and ($_.Split(':')[1].Split('@')[1] -notin $Domains) }
    If ($ExternalAddresses) {
        $ReportLine = [PSCustomObject][Ordered]@{
            DisplayName             = $Mailbox.DisplayName
            PrimarySmtpAddress      = $Mailbox.PrimarySmtpAddress
            EmailAddresses          = $ExternalAddresses -join ", "
            Type                    = "mailbox"
            Identity                = $Mailbox.Alias
        }
        $Report.Add($ReportLine)
    }
}
 
Write-Host "Checking Microsoft 365 Groups..."
[array]$Groups = Get-UnifiedGroup -ResultSize Unlimited
 
ForEach ($Group in $Groups) {
    $ExternalAddresses = $Group.EmailAddresses | Where-Object { $_ -like "SMTP:*" -and ($_.Split(':')[1].Split('@')[1] -notin $Domains) }
    If ($ExternalAddresses) {
        $ReportLine = [PSCustomObject][Ordered]@{
            DisplayName             = $Group.DisplayName
            PrimarySmtpAddress      = $Group.PrimarySmtpAddress
            EmailAddresses  = $ExternalAddresses -join ", "
            Type                    = "group"
            Identity                = $Group.Alias
        }
        $Report.Add($ReportLine)
    }
}
 
Write-Host "Checking Distribution Lists..."
[array]$DLs = Get-DistributionGroup -ResultSize Unlimited
 
ForEach ($DL in $DLs) {
    $ExternalAddresses = $DL.EmailAddresses | Where-Object { $_ -like "SMTP:*" -and ($_.Split(':')[1].Split('@')[1] -notin $Domains) }
    If ($ExternalAddresses) {
        $ReportLine = [PSCustomObject][Ordered]@{
            DisplayName             = $DL.DisplayName
            PrimarySmtpAddress      = $DL.PrimarySmtpAddress
            EmailAddresses          = $ExternalAddresses -join ", "
            Type                    = "dl"
            Identity                = $DL.Alias
        }
        $Report.Add($ReportLine)
    }
}
 
Write-Host "Checking Dynamic distribution groups..."
[array]$DDLs = Get-DynamicDistributionGroup -ResultSize Unlimited
 
ForEach ($DDL in $DDLs) {
    $ExternalAddresses = $DDL.EmailAddresses | Where-Object { $_ -like "SMTP:*" -and ($_.Split(':')[1].Split('@')[1] -notin $Domains) }
    If ($ExternalAddresses) {
        $ReportLine = [PSCustomObject][Ordered]@{
            DisplayName             = $DDL.DisplayName
            PrimarySmtpAddress      = $DDL.PrimarySmtpAddress
            EmailAddresses          = $ExternalAddresses -join ", "
            Type                    = "ddl"
            Identity                = $DDL.Alias
        }
        $Report.Add($ReportLine)
    }
}
 
Write-Host ("{0} mailboxes, {1} groups, {2} distribution lists, and {3} dynamic distribution lists checked" -f $Mailboxes.Count, $Groups.Count, $DLs.Count, $DDLs.Count)
Write-Host ("Problems found in {0} objects" -f $Report.Count)
 
$Report | Format-Table -AutoSize
 
ForEach ($Object in $Report) {
 
    $UpdatePrimary = $false
    $NewPrimarySmtpAddress = $null
 
    # Check if primary SMTP address needs to be updated
    If ($Object.PrimarySmtpAddress.Split('@')[1] -notin $Domains) {
        Write-Host ("Primary SMTP address must be updated from {0}" -f $Object.PrimarySmtpAddress)
        $NewPrimarySmtpAddress = ("{0}@{1}" -f $Object.PrimarySmtpAddress.Split('@')[0], $PrimaryDomain)
        $UpdatePrimary = $true
    }
 
    If ($UpdatePrimary) {
        Write-Host ("Setting new primary SMTP address {0}" -f $NewPrimarySmtpAddress)
        Switch ($Object.Type) {
            "mailbox" {
                Set-Mailbox -Identity $Object.Identity -EmailAddresses @{Remove=$Object.PrimarySmtpAddress; Add=$NewPrimarySmtpAddress} -ErrorAction SilentlyContinue
                Set-Mailbox -Identity $Object.Identity -WindowsEmailAddress $NewPrimarySmtpAddress -ErrorAction SilentlyContinue
            }
            "group" {
                Set-UnifiedGroup -Identity $Object.Identity -PrimarySmtpAddress $NewPrimarySmtpAddress -ErrorAction SilentlyContinue
            }
            "dl" {
                Set-DistributionGroup -Identity $Object.Identity -PrimarySmtpAddress $NewPrimarySmtpAddress -ErrorAction SilentlyContinue
            }
            "ddl" {
                Set-DynamicDistributionGroup -Identity $Object.Identity -PrimarySmtpAddress $NewPrimarySmtpAddress -ErrorAction SilentlyContinue
            }
        }
    }
 
    [array]$EmailAddresses = $Object.EmailAddresses -split ", "
    ForEach ($Address in $EmailAddresses) {
        If ($Address.Split('@')[1] -notin $Domains) {
            $AddressToRemove = $Address.Split(':')[1]
            Write-Host ("Removing address {0} from {1}" -f $Address, $Object.DisplayName)
            Switch ($Object.Type) {
            "mailbox" {
                Set-Mailbox -Identity $Object.Identity -EmailAddresses @{Remove=$AddressToRemove} -ErrorAction SilentlyContinue
            }
            "group" {
                Set-UnifiedGroup -Identity $Object.Identity -EmailAddresses @{Remove=$AddressToRemove} -ErrorAction SilentlyContinue
            }
             "dl" {
                Set-DistributionGroup -Identity $Object.Identity -EmailAddresses @{Remove=$AddressToRemove} -ErrorAction SilentlyContinue
            }
             "ddl" {
                Set-DynamicDistributionGroup -Identity $Object.Identity -EmailAddresses @{Remove=$AddressToRemove} -ErrorAction SilentlyContinue
            }
            }
        }
    }
 
}
Write-Host "All done"