We have a variety of e-newsletters. Some clients send us 3rd party click tags, rather than traditional images. We receive a variety of tags from different ad servers such as Doubleclick. On the e-newsletters, some tags track the click throughs and others do not. We ran some tests and found we can use a click tracker tag + an image file or a click tracker tag + a standard href tag. We are able to get the ad to display, and the click and track on our end. However, there are times when clients tell us the tags are not tracking. I'd like suggestions on what types of click tags to stay away from in Email marketing. What types of click tags work? What guidelines should I include in our terms & conditions?