SendGrid can track when the emails are opened:
How to get a notification (via email) when emails are opened, for which the recipient is different to [email protected]? (I don't want to receive a notification when I open my own emails sent to myself as BCC).
Do I need to use the SendgridAPI? How? Can I ask Sendgrid to send a notification? (To my server, who will send the notification? To something else?)

