Yes, take the email or they should actually have attached a more formal version of it. This is where immigration can see your visa issue and expiry dates, etc. And can verify it by scanning the QR code on it.
The stamp in your passport is just your entry stamp. They always write the basis on entry - Non O, TR, OA, etc and when it's an e-visa they write that as well, but the stamp itself is not a visa.