[jjeaff]

Delivery success is usually based on the download of a tracking pixel. Problem is, Gmail downloads and proxies all images (including those tracking pixels). So anything that doesn't get completely filtered out before showing up in the inbox or spam box is going to be seen as -received- by, as far as I know, any software out there.

There are quite a few messages that never even make it to the spam box, which I have never understood because plenty of very obviously sketchy spam messages get through to my spam box. Yet, occasionally we have trouble getting very legitimate transactional emails through to some customers.