Guild Wars 2

1: Make it so that to add a player to a friends list requires their authorisation.
2: Make it so that email can only be received from friends.

Doesn’t kill the problem completely, but should help massively.

Maybe make it so that when people who aren’t on your friends list send you mail, it costs them money.
If I remember correctly, EVE Online has a system like this, and it even allows players to set the cost of the cost of sending them mail. I would imagine that if players made it so that non-friends mailing them had to spend 10g a pop, the problem would quickly solve itself.
Just a crazy idea. Later.

1) when they add you, they are followers of you, not friends. Only when you add them also, they are friends.
2) that way you never can resieve gifts from guildies that are not friends

2. not just from friends, also from guild members

Sounds like a good idea, especially the part where you can choose how much it costs to mail you. (Within limits of course)