This is just an idea I have been thinking about so I thought I would throw it out there. While the mail system is handy for communicating with others, sending items and such, I feel it is kind of bland the way it is presented currently. I think a more personalized option would improve the mail system.
My idea is for Anet to implement a system that would add some flavor to player to player mails. What I think would be interesting would be an optional postcard system of sorts. I'm going to present two separate versions. The first is more complex and probably not very likely due to that but I think it would be the neatest way to implement it. The second version is less complex and would still allow a more personal touch to be added to player mail. I'll present the two ideas with benefits and potential problems I can think of.
Version 1: The more complex version, a postcard with a player selected screenshot ("selfie").
This would allow players to take a screenshot in game that is "printed" on a postcard with a personalized message. When the recipient opens the mail a postcard will appear on screen with the message and any items and coin attached (like normal mail). I created an example and included it below. The benefit is this allows the sender to make the mail sent more personal and visually interesting. Adding images to the postcard from the player's travels and adventures would be fun in my opinion.
However, I imagine this would be difficult for Anet to implement as they would have to design a system that would allow the player to take a selfie within specific dimensions. It would probably have to be a rather complex UI that allows the player to preview the selfie, crop, and reposition the image within the defined space. Additionally to avoid players adding thousands of screenshot "selfie" images to Anet servers there would have to be a limit or maybe even only one at a time where the image is overwritten should the player want to change it. This limit could be problematic as to what happens to the custom image in mails sent prior to changing it. I imagine it would have to change as well to again avoid Anet storing countless custom mail images on their server. Players may not find this limitation favorable.
Example of a postcard as it would appear on the screen:
Anet could sell a "selfie stick" for players to include custom in game screenshots on their postcard. Note only in game screenshots directly uploaded from within the game could be added to the postcard and no images uploaded from the player's computer. This would avoid players adding images that are against TOS.
Version 2: Premade postcards created by Anet.
In this version the postcard works as above as in it displays on the screen when the mail is opened but images would be limited to what Anet provides. With this the player could select from a group of postcards they have obtained. This would be like a skin for your mail. They would appear similar to the example above but with an image created by Anet instead of a player screenshot. The benefit of this version is that players could still add flavor to the mails they send but there would be no need for a more complex "selfie" system. So for example Anet could sell themed sets of postcards the player could choose from when sending mail. There could be seasonal sets, sets based on living story, etc. There could even be postcards you earn that pay tribute to certain achievements. As for problems, as with version 1, Anet would have to make changes to the mail UI for this to work and I don't know if that is possible.
Additionally with both versions there would probably have to be a stricter character limit for text in the postcard mails. This is due to the image(s) taking more space. In this case there would need to be an option to send a normal mail, as is currently in game, or the postcard mail limited to less characters. Again this would make the necessary changes to the mail UI more complex.
In a game where customization and imagery is so significant I find the current mail system rather bland and impersonal. I would like to see this changed to something more interesting and fun for the players. I feel some version of the above suggestion would be a benefit to players and Anet. Of course it could be monetized like mount skins, outfits, etc.
Pros: More colorful and and customizable appearance of mail as selected by the player. Something Anet could monetize.
Cons: Work from Anet to alter the mail UI to accommodate the postcard system. This could be a significant amount of effort and may not even be possible with the current structure of the existing game code. A potential more significant limit to the amount of text players could include when sending the postcard version of a mail.
Lastly, I am aware that Anet has a lot of more important things to work on than what in game mail looks like. I don't even know if many players send enough mail to be interested in a more customizable appearance of the mail they send. But in my opinion it is a fun concept that some day could be added to the game if possible.
Note: To the best of my knowledge there is no actual player with the display name of Every GW2 Player.1234 Also no quaggans were harmed while making the postcard stamp.