Macro, Auto, Email, Date

Using Excel Office 365. This is the Module. I'm sure it is something very simple but it is driving me crazy. It sends the email perfectly when I hit "run" from Developer, Macros. I need it to run when the Workbook opens. This code is in a module for "Sheet 16". The dates are in the two columns. Thanks for your help.

Option Explicit

Sub email()

    Dim r As Range
    Dim cell As Range

    Set r = Range("D3:D300", ["G3:G200"])
    For Each cell In r

        If cell.Value = Date Then

    Dim OutApp As Object
    Dim OutMail As Object
    Dim strbody As String

    Set OutApp = CreateObject("Outlook.Application")
    Set OutMail = OutApp.CreateItem(0)

    strbody = "SOW OUT - SOW NEW D & G"
    On Error Resume Next
    With OutMail
        .To = "gaias@comcast.net"
        .CC = "online2007@comcast.net"
        .BCC = ""
        .Subject = "ALERT"
        .Body = strbody
        .Send
    End With
    On Error GoTo 0

    Set OutMail = Nothing
    Set OutApp = Nothing
End If

Next

    Exit Sub

debugs:
        If Err.Description <> "" Then MsgBox Err.Description

End Sub