When using multiple accounts, how to ensure emails are sent from the correct account

I've seen variations of this question before, but can't find any now so figured I'd ask and answer it.

I wrote this VBa to resolve the issue! Now when I click send, if I'm not sending from a specific account it will look through the 'send to list' and then prompt me to either cancel or continue. This means it's wonderfully non-invasive! If I click cancel (do not send), the email remains open and unchanged.

Open the developer ribbon, open Visual Basic. Open the 'ThisOutlookSession' and paste in the following code

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

Dim oMail As MailItem
  Set oMail = Item

  Dim shouldSend As Boolean
  shouldSend = ShouldSendEmailFromBusinessAccount(oMail)
If Not (shouldSend) Then
    MSG1 = MsgBox("Are you sure you want to send this from the account you're using?", vbYesNo, "Are you sure?")
End If

If MSG1 = vbNo Then
    Cancel = True
End If

'Cancel = True

End Sub

Private Function ShouldSendEmailFromBusinessAccount(ByVal oMail As MailItem) As Boolean

    ShouldSendEmail = True

 'Set the recipients domains/email addresses you want to check.
    Dim sendToEmails(0 To 2) As String
    sendToEmails(0) = "@domain.co.uk" ' block a domain by TLD
    sendToEmails(1) = "domiain2" ' block an entire domain
    sendToEmails(2) = "[email protected]" ' block a person



'The only account you want to send emails to
    Dim theAccountsToSendEmailsFrom(0 To 0) As String
    theAccountsToSendEmailsFrom(0) = "[email protected]"

    Dim recCount As Integer
    Dim myRec As Outlook.Recipient
    Dim mySender As String

    mySender = oMail.SendUsingAccount

    For a = 0 To UBound(theAccountsToSendEmailsFrom)

    theAccountToSendEmailsFrom = theAccountsToSendEmailsFrom(a) ' note, one is plural

        If (InStr(mySender, theAccountToSendEmailsFrom) = 0) Then

            recCount = oMail.Recipients.Count
            For i = 1 To recCount

                Set myRec = oMail.Recipients(i)
                myAddress = myRec.Address

                For j = 0 To UBound(sendToEmails)
                    If (InStr(LCase(myAddress), LCase(sendToEmails(j)))) Then
                        MsgBox ("Ooops, you are going to send to: " & sendToEmails(j) & " from " & mySender)
                        ShouldSendEmail = False
                        Exit For
                    End If
                Next

            Next
        End If

    Next

    ShouldSendEmailFromBusinessAccount = ShouldSendEmail

End Function

Since I only want to send to the domains from my work account, if I try to send from any other, I get:

Otherwise, it will just send as normal.

The above code will check every outgoing email address! This means it will check the To, CC and BCC... As soon as it finds a single recipient which matches, it will then show the Prompt asking if you want to send or not.