Sending Email to 'X' users with an e-mail attachment

I have a list of email address from A1 to A100 and I'm attempting to use VBA to send out the emails with an attached workbook. I'm using MS Outlook 2003 SP3.

With a little shuffling over the net, I've been able to craft up my procedure to look like this:

Public Sub Send_Email()

Dim r1 As Range

Set r1 = ThisWorkbook.Sheets(1).Range("A1")
Set last_row = r1.End(xlDown)

Do While r1.Address <> last_row.Offset(1, 0).Address
   
    Set objOutlook = CreateObject("Outlook.application")
    Set objNameSpace = objOutlook.GetNamespace("MAPI")
    Set MItem = objOutlook.CreateItem(olMailItem)
   
    MItem.To = r1.Value
    MItem.Subject = "Subject Goes here"
    MItem.Body = "I'm sending this email now"
    MItem.Attachments.Add ActiveWorkbook.FullName
    MItem.Save
    MItem.Send
   
    Set objOutlook = Nothing
   
Set r1 = r1.Offset(1, 0)
Loop

End Sub

The issue is the screenshot as shown in the enclosed attachment. I keep getting the annoying box "A program is trying to automatically send e-mail on your behalf. Do you want to allow this? If this is unexpected, it may be a virus and you should choose "No" ".

While I understand the reason for this menu item, I want to bypass it OR find a completely different workaround by adding to the above procedure. I'm fine with pressing the 'Yes' button in the enclosed attachment once. But I can't keep doing it for every single person in the list (I simply have too many).

I did look online for workarounds and apparently there are free click-yes tools that press the yes for you every single time. I am not allowed to download ANYTHING on my machine primarily because its unsafe.

Can you please help? THIS IS URGENT!