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In a Module:
Code:
Sub Main()
  Dim c As Range, f As Range, source As Worksheet, master As Worksheet, s As String
  'Add reference: Microsoft Outlook xx.x Library, where xx.x is 14.0, 15.0, 16.0, etc.
  Dim olApp As Outlook.Application, olMail As Outlook.MailItem
  
  Set source = Worksheets("Request List")
  Set master = Worksheets("Master List")
  Set olApp = New Outlook.Application
  
  For Each c In source.Range("A2", source.Cells(source.Rows.Count, "A").End(xlUp))
    With c
      If .Offset(, 2).Value <> "NO" Then GoTo NextC
      If .Offset(, 4).Value <> True Then GoTo NextC
      
      Set f = master.Range("A:A").Find(c.Value)
      Set olMail = olApp.CreateItem(olMailItem)
      With olMail
        .To = f.Offset(, 3).Value                             'Master Column D
        .CC = f.Offset(, 5).Value                             'Master Column E
        .Subject = "Catalog Request: " & c.Offset(, 1).Value  'Source Column B
        'Build body string:
        s = "Hello " & f.Offset(, 1).Value & "," & vbCrLf & vbCrLf
        s = s & "May you please send the Subsidiary Catalog List for " & _
          c.Offset(, 1).Value & "?" & vbCrLf & vbCrLf
        s = s & "Thanks you," & vbCrLf & vbCrLf
        s = s & "sig data..."
        .Body = s
        .Display
        '.Send
      End With
      .Offset(, 2).Value = "YES"  'Source sheet sent, YES.
      .Offset(, 3).Value = Date   'Source sheet, Date sent.
    End With
NextC:
  Next c
  
  On Error Resume Next
  Set olMail = Nothing
  Set olApp = Nothing
End Sub