RetroGaming

The best non-WEGO turnbased tactics game ever, winSPMBT/winSPWW2 (a descendent of Steel Panthers) is still in development and play by email is the main method of multiplayer.

https://www.shrapnelgames.com/Camo_Workshop/MBT/MBT_page.html

https://www.shrapnelgames.com/Camo_Workshop/WW2/WW2_page.html

Also, check out modern board games and their digital implementations, Yucata is great.

https://www.yucata.de/en

For board games in particular I recommend both the digital and physical versions of Scythe for the vibes you are talking about.

https://boardgamegeek.com/boardgame/169786/scythe

https://store.steampowered.com/app/718560/Scythe_Digital_Edition/

Also the Pandemic Legacy series of board games.

https://boardgamegeek.com/boardgame/161936/pandemic-legacy-season-1

Definitely check out the Vassal engine which is an open source board game/wargame engine with a massive library of games and play by email functionality.

https://vassalengine.org/

https://vassalengine.org/library/projects

If you liked Advanced Wars try out Advance Wars By Web

https://awbw.amarriner.com/

Lastly, if the rabbit hole of train games seems appealing the 18xx website looks great...

https://18xx.games/

Want to spend 6 months learning a game and still only scraping the surface of a gigantic logistics simulator? May I introduce you to Gary Grigsby's War in the Pacific: Admirals Edition

Check out Your Turn, you play a retro game using a supported emulator and use this app to pass the save file back and forth to the other players.
Currently Android only, hopefully a PC version will come out in the future.

Shoutout to PerfectDark for posting about it.

That sounds like so much fun. My college’s email game was someone accidentally mass emailed to the whole school roster and everyone replied with a smartass comment until it got shut down lol.

Happened a few times a semester, too.

There are a lot of great digital board game adaptations with asynchronous multiplayer. Terraforming Mars, Lords of Waterdeep, and Scythe, to name a few.

Probably not exactly what you're looking for, but Board Game Arena is pretty good for asynchronous multiplayer, though as you might be able to guess from the name it's digital versions of tabletop games rather than normal video games

Really interesting, because just a while ago I remembered my experience of playing VGA Planets at the local BBS during my school years in early-mid 1990s. (This is a turn based game where people would submit their turn files, the arbitrator software thing would do its thing weekly, and we'd download the results.) The sysop was a classmate and, since the international money transfers were complicated for school kids at the time, organised getting everyone a registered copy in bulk. I do remember I said something in global messages and people thought it was, in modern vernacular, cringe. I don't remember how the game ended up. I played some underwhelming race. I can't remember.

The chess.com app has support for this kind of thing.

Also, I strongly recommend the game Subterfuge: subterfuge-game.com

The game takes place in real time, sending your ships to capture nodes or building resources, but these actions take a long time to complete (for example, it might take 10 hours for a ship to travel between two nodes). The game has a scheduling system, so typically you make moves in real-time, instead you check in every few hours and schedule some moves in advance.

https://archipelago.gg/ is not the same thing, but you can set up a multi-person, multi-game asynchronous randomizer that usually lasts for days because Link's sword is in the Marsh Cave, but to get to the Marsh Cave you need the ship and the ship is in Pewter Gym....