Do you know where I could go to find people who are playing it through email?

I used to play at DipWorld, but it looks like it's a lot less active lately. It appears that the most active community now is at the Diplomatic Pouch. The site design leaves something to be desired, but after some clicking around, this appears to be a decent place for a new player to start: http://www.diplom.org/Email/

It's been years but http://www.redscape.com/ is one location to play by email.

Personally I play a bit on my phone using the Droiddippy app. However you can also play via web at http://droidippy.oort.se/web.