Detect image rendering in email

Question

I know that services like SendGrid already have built-in plugins for this. But I want to build my own, custom, module for this.

Reason why I am doing this is my application uses several different smtp servers specified by user.

Is it even feasible to create one module for different smtp servers?

Answer 1

Absolutely! It's relatively simple too, at the most basic level you do the following:

• Assign every email you send a unique id, in the email place a reference to a script on your server with the unique id. (e.g. <img src="https://example.com/img?id=1 >)
• When /img?id=N is called have your code log the id and then serve the image.

A more concrete example in PHP would look something like:

Mail Sender:

$img = '<img src="https://example.com/img.php?id=' . generate_email_id() . '">';
mail("test@example.com", "This is a test.", "Hello! I hope this test works!" . $img);

img.php:

log_email_by_id($_GET['id']);
header("Content-type: image/jpeg");
readfile("pixel.jpg");