I've lost count of the number of times I've wanted to forward a mail to someone else, only to end up copying and pasting the whole thing instead.
Whether it's a guide, recruitment message, event information, trade details or just something useful another player has sent you, being able to simply click Forward would save a lot of time.
The forwarded mail could include something like:
Forwarded from: PlayerName
Original date: xx/xx/xxxx
This keeps the original formatting and also shows where the message came from.
As a faction leader, I run into this quite a bit. Sometimes a member sends me something I'd like to pass on to the rest of the faction, or another faction sends information that's worth sharing. At the moment the only option is to copy everything manually, which is a bit clunky.
This wouldn't just benefit faction leaders either. Traders, recruiters, mentors and regular players would all find uses for it.
It's not a massive feature or anything game changing, just a simple quality of life improvement that feels like it should already exist.