Apparently ID3 included some strange frames such as the Popularimeter (POPM) for storing emails and ratings! lawik goes through some om them in this post which I found entertaining.
I came across his article about a month ago and likewise enjoyed it. I was a little disappointed (but only a little) when I discovered afterwards that his suggestion of using event time codes to set off explosives on stage was actually suggested in the ID3v2 standards themselves!
The fanciful ideas on the POPM frame were very interesting. The ID3v2 standards author's late 1990s, pre-massive-spam-onslaught design choice to include an email address seems kind of quaint now!
https://underjord.io/id3-specification-and-speculation.html