I've been having a bad time with email of late. It's been the method of communication between us and another company (a pretty creaky old product). I thought they were replying strangely and ignoring my questions "did they even read what I said!?". It turns out for whatever reason they hadn't been getting some of my emails.

Now I can't trust that anything has been received unless I get an acknowledgement, so I have to keep pestering for replies. Basically lost trust in the protocol because it's dependent on the the other person's mailserver behaving they way you expect it to.