I send over 1M transactional (user opt in only) emails per day for one of my websites. We have to be pretty strict how we handle bounces and complaints or it c

I send over 1M transactional (user opt in only) emails per day for one of my websites. We have to be pretty strict how we handle bounces and complaints or it can tarnish our sending rep. Sometimes people accidentally flag mail as spam, or maybe their client does, or maybe their server does, and this comes back to us as a complaint. Under the ToS of my email gateway I must stop sending to that address until the user updates their email. There is a lot of assumptions in this post about tracking pixels etc, without any concrete evidence. The truth could be far simpler.