Capture LegacyExchangeDN's during Exchange org splits

Capture-LegacyExchangeDNs.ps1

<#
    .Synopsis
    This is not intended to be an executable script.  It's PS1 for now simply for syntax highlighting.
#>

#======#---------------------------#
#region# Backup LegacyExchangeDN's #
#======#---------------------------#
$LDNRecipients = @()
$Recipients = @()
$Recipients += Get-Mailbox -ResultSize Unlimited -WarningAction SilentlyContinue -ErrorAction SilentlyContinue
$Recipients += Get-RemoteMailbox -ResultSize Unlimited -WarningAction SilentlyContinue -ErrorAction SilentlyContinue
$Recipients += Get-DistributionGroup -ResultSize Unlimited -WarningAction SilentlyContinue -ErrorAction SilentlyContinue

foreach ($rcpt in $Recipients) {

    $_x500s = @("X500:$($rcpt.LegacyExchangeDN)")
    $_x500s += $rcpt.EmailAddresses | Where-Object { $_ -like 'X500:*' }
    $LDNRecipients += [PSCustomObject]@{

        RecipientTypeDetails = $rcpt.RecipientTypeDetails
        DisplayName          = $rcpt.DisplayName
        PrimarySmtpAddress   = $rcpt.PrimarySmtpAddress
        X500Addresses        = $_x500s -join '|||||'
    }
}

$LDNRecipients | Export-Csv "$($HOME)\Desktop\$([datetime]::Today.ToString('yyyy-MM-dd'))_LegacyExchangeDNs_for_FWD-Contacts.csv" -NTI -Encoding UTF8
#=========#---------------------------#
#endregion# Backup LegacyExchangeDN's #
#=========#---------------------------#



#======#----------------------#
#region# Create MailContact's #
#======#----------------------#
# Set a static DC to use for both the New-MailContact and follow-up Set-MailContact command:
$DomainController = "<DC FQDN>"

# Specify the OU wherein to create the MailContacts:
$TargetOU = "<domain.tld/OU1/OU2/OU3>"

$CreateContacts = Import-Csv "<Full/relative file path to CSV>"
foreach ($Contact in $CreateContacts) {

    # Create the contacts:
    try {
        $newMailContactParams = @{

            Name                 = $Contact.DisplayName
            ExternalEmailAddress = $Contact.PrimarySmtpAddress
            OrganizationalUnit   = $TargetOU
            DomainController     = $DomainController
            ErrorAction          = 'Stop'
        }
        New-MailContact @newMailContactParams
    }
    catch {
        Write-Warning -Message "Failed to create MailContact for '$($Contact.DisplayName)' ($($Contact.PrimarySmtpAddress)).  Error:`r`n$($_.Exception)"
    }

    # Add the LegacyExchangeDN's as X500's to the contacts:
    try {
        $setMailboxContactParams = @{

            Identity                      = $Contact.PrimarySmtpAddress
            EmailAddresses                = @{Add = @($Contact.X500Addresses -split '\|\|\|\|\|') }
            HiddenFromAddressListsEnabled = $true
            DomainController              = $DomainController
            ErrorAction                   = 'Stop'
        }
        Set-MailContact @setMailboxContactParams
    }
    catch {
        Write-Warning -Message "Failed to add X500 addresses to '$($Contact.DisplayName)' ($($Contact.PrimarySmtpAddress)).  Error:`r`n$($_.Exception)"
    }
}
#=========#----------------------#
#endregion# Create MailContact's #
#=========#----------------------#