Compare columns in different worksheets nad highlight differences

Untested, give this a try

Sub FindEmail()
Const shLarge As String = "Sheet1"    '<=== big spreadsheet sheet name. Change for you needs
Const shOther As String = "Sheet2"    '<=== small spreadsheet sheet name. Change for you needs
Dim FoundCell As Range, rng As Range, c As Range

    With Worksheets(shLarge)
        Set rng = .Range("c2", .Cells(Rows.Count, "c").End(xlUp))
        For Each c In rng
            Set FoundCell = Worksheets(shOther).Range("F:F").Find(What:=c.value, LookAt:=xlWhole)
            
            If FoundCell Is Nothing Then
                c.Interior.Color = vbYellow
            End If
        Next
    End With
    
End Sub