Tracking open rates using sendmail

Question

Does anyone know of a cheap and easy way to capture open rates via sendmail, without leveraging Mandrill, mailchimp, etc?

Answer 1

This is unlikely to exist, at least as a simple extension to sendmail. The primary reason for that is that it requires tight integration with your sending application. For starters, your application would need to produce email payloads that include a unique-per-recipient tracking images then you'd also need a system to record the requests for those images and associate them back to the original sending.

On top of all that: one major benefit of an email service provider is that they take care of the reputation of their sending IP addresses, making their mail more likely to get past the spam filters of major email services.