Summary
Players need a better way to celebrate positive moments among friends and FC members. Adding stationery would be an easy way to achieve this, with minimal impact on the design team, while building on already-existing tech, and creating a gil sink.

Explanation:
As a player, I often want to cheer up or cheer on FC members or friends. However, the simple / standard gray background that exists within the in-game mail doesn't let me do this effectively (no colorful backgrounds, stickers, etc.). No matter how I try, the message feels very basic for such a frequently used feature - and after all, words can only get you so far.

Stationery - mail that functions like normal in-game mail, but with a simple special background - could allow players to celebrate positive moments better. For example:

* Fellow FC members going through a rough time, lending support, "I'm thinking of you"
* Congratulating friends for reaching the end of the MSQ, "you did it, high five!"
* Welcoming returning players - "Missed you, so happy you're back - let's adventure together, I'll help you get caught up, just let me know!"

This could be a great thing for players to encourage one another, helping them feel good for returning to the game, or hitting in-game goals, and letting the game have a more positive / pro-social effect on their mental health and well being.

I think it also makes sense purely from a design perspective:

* Stationery could be sold by in-game vendors for a small gil fee, may 100g per letter - fancier stationery (more elaborate backgrounds) could cost a bit more, maybe 500g to 1000g - serving as a useful additional gil sink

* You could demo this concept by starting with Adventurer Plate backgrounds - these already exist, and importing those assets into the mail system means you're expanding an existing feature's functionality, rather than having to build anything from scratch

* If players like the feature, there are many ways to scale / expand it - e.g. adding stickers, backgrounds with simple animations, etc. Think postcards, but with 1-2 extra little things that bring it to life a bit. All of it 2D and simple to animate. Maybe for a bit more gil, people could send their own custom background as a "signature" letter style, much like Adventurer Plates?

* If there is a news feed added to the game at some point that calls out what your friends or FC members achieved organically to players, this could also tie into that

I think this is a win for players and the game itself on several levels, without asking too much of the design / UI teams, and in the end creating a new means of expression and well-wishing in the game that also acts a helpful gil sink.

Thank you for considering my feedback!