In ECM 2.2, the RegisterEmailOpened.aspx was located in sitecore_modules directory, which is mapped to the Sitecore site "modules_shell". In EXM 3.3, this page is moved to /sitecore/ and made an ashx. Okay, cool...
Method #1: Use URL Rewrite to redirect to the new location. For whatever reason, whether it's stupidity or lack of regex understanding, I could not get a rewrite rule to redirect. Aborted.
Method #2: Created an aspx page in the same location to force a redirect. Turns out, this is the method I REALLY want to do, because before doing the redirect, I've realized that I need to do work to convert the query params from ECM 2.2 to EXM 3.3 query params before going to the new EXM 3.3 location -- Therefore, this is actually the method I want to use. but having complications.
Issue: The complications are that I need to instantiate the Sitecore Analytics Tracker in order to identify the user and create an Xdb Contact record if one doesn't exist. But "modules_shell" has EnableTracking set to false in the Site Definition.. (to wit I'm assuming is for a reason), meaning that the "startAnalytics" pipeline aborts out before creating the Tracker.
Research: I thought it was because I have a blank for Analytics.The hostname for the longest, but it's actually not even getting to that point. That may still be an issue, and figuring out how I need to set Analytics.Hostname for a multisite environment is my next research question.
Is there any reason why I WOULDN'T want to set EnableTracking true on the modules_shell site in Sitecore?