User blog comment:Kirkburn/Technical Update: April 13, 2015/@comment-452-20150418194704/@comment-166269-20150419015531

While I can't speak to plain-text emails, I will note that Wikia's HTML emails have used those tracking URLs for as long as I can remember; they're nothing new.

I have always been curious what the information in the URL decodes to, though: looking at it now, I can tell the string is two base64-encoded strings, but they both decode to binary gobbledygook.