You can specify that you want a read or delivery receipt, but if the recipient is like me, I just ignore those requests so you will never know if I have read it. Delivery is a little different, and you really don’t need to select that option as you can assume every message has been delivered unless you get a server reply that it could not be delivered.
Before sending you messages, click the More button and select what you need.
Spammers often put a single-pixel linked image in the message, and as soon as it is opened by the recipient, the link connects to a server. That way they know if the address is valid and the message has been opened. But I don’t recommend that.