Hi,
I’m building an invoicing app for my users from which they can send out the invoices via email using the Sendgrid plugin. For this I have a Sendgrid account and dynamic templates. The emails are sent out succesfully, however now I would like to include the “open tracking” of emails that my users send out (e.g. when a user sends an invoice to his/her customer and he/she opens the email, my user sees this in his dashboard when he clicks on the invoice information).
Has someone got the necessary knowledge (API,…) in order to help me implement this in my application?
Big thanks upfront! 
Kind regards,
Gerben