Warn before sending messages outside of multiple possible internal domains?

I'm trying to check if recipients of my e-mail are in our Global Address List in Outlook 2016.

If all the recipients are internal (our GAL includes only internal addresses) then the message is released.

If at least one of the recipients are external (from outside of GAL), then I should get a warning message, which will ask if I still want to send this e-mail.

I tried this topic, but I need a solution without copying the addresses to external Excel spreadsheet.

I also worked with this solution, but our company is big, and has multiple branches all around the globe. The cited solution checks if my domain is the same with the recipients domains. The problem occurs when I'm trying to send an e-mail to people from my company, but outside my region - I'm from EMEA, and e.g. I'm sending an e-mail to PAM. Unfortunately, this solution is not enough in this moment. Because PAM is using a different domain - the warning message occurs.

The simplest way for me, would be to check the recipients in GAL, but I'm not sure if this is even possible.

Code from the second solution below:

Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean)
 Dim recips As Outlook.Recipients
 Dim recip As Outlook.Recipient
 Dim pa As Outlook.propertyAccessor
 Dim prompt As String
 Dim Address As String
 Dim lLen
 Dim strMyDomain
 Dim internal As Long
 Dim external As Long

Const PR_SMTP_ADDRESS As String = "http://schemas.microsoft.com/mapi/proptag/0x39FE001E"

' non-exchange
' userAddress = Session.CurrentUser.Address
' use for exchange accounts
userAddress = Session.CurrentUser.AddressEntry.GetExchangeUser.PrimarySmtpAddress
lLen = Len(userAddress) - InStrRev(userAddress, "@")
strMyDomain = Right(userAddress, lLen)

Set recips = Item.Recipients
 For Each recip In recips
 Set pa = recip.propertyAccessor

Address = LCase(pa.GetProperty(PR_SMTP_ADDRESS))
 lLen = Len(Address) - InStrRev(Address, "@")
str1 = Right(Address, lLen)

  If str1 = strMyDomain Then internal = 1
  If str1 <> strMyDomain Then external = 1
Next

 If internal + external = 2 Then
prompt = "This email is being sent to Internal and External addresses. Do you still wish to send?"

 If MsgBox(prompt, vbYesNo + vbExclamation + vbMsgBoxSetForeground, "Check Address") = vbNo Then
    Cancel = True
 End If

End If

End Sub

Solution

You could replace the single internal domain with an array of domains.

Option Explicit

Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean)

    Dim recips As Recipients
    Dim recip As Recipient

    Dim pa As propertyAccessor

    Dim prompt As String
    Dim Address As String

    Dim lLen As Long
    Dim Str1 As String

    Dim arrayDomains() As Variant
    Dim i As Long

    Dim internalFlag As Boolean
    Dim externalFlag As Boolean

    Dim strExtAdd As String

    arrayDomains = Array("PAM domain", "EMEA domain", "other internal domain")

    Const PR_SMTP_ADDRESS As String = "http://schemas.microsoft.com/mapi/proptag/0x39FE001E"

    Set recips = Item.Recipients

    For Each recip In recips

        Set pa = recip.propertyAccessor

        Address = LCase(pa.GetProperty(PR_SMTP_ADDRESS))
        lLen = Len(Address) - InStrRev(Address, "@")
        Str1 = Right(Address, lLen)

        internalFlag = False

        For i = LBound(arrayDomains) To UBound(arrayDomains)
            If Str1 = arrayDomains(i) Then
                internalFlag = True
                Exit For
            End If
        Next

        If internalFlag = False Then
            externalFlag = True
            strExtAdd = strExtAdd & vbCr & Address
        End If

    Next

    If externalFlag = True Then

        prompt = "This email is being sent to external addresses. Do you still wish to send?" & strExtAdd
        If MsgBox(prompt, vbYesNo + vbExclamation + vbMsgBoxSetForeground, "Check Address") = vbNo Then
            Cancel = True
        End If

    'Else

        'Debug.Print "Internal addresses only."

    End If

End Sub