Ability to leave a message for offline players

Okay, here's an idea; could Guild Leaders and Officers get the ability to leave a message for a player that's offline, that will pop-up when the next time player comes online. To stop abuse and spammage it would be limited to members of the Guild/Alliance.

I'm in an international Guild, and catching certain players online to inform them of something is a bit of a pain sometimes. A message service would help a lot.

/signed for people in guild only. Outside of that it has massive potential for abuse.

/signed for guildies/friends. I have many friends that arent in my guild, and i would want to be able to leave messages for them too. Or you could send someone an "invite" to be able to send you messages.

/signed for guildies/friends.

Or maybe a tickbox like;

[ ]Guildies
[ ]Friends
[ ]Alliance members
[ ]All players

Which lets you tick certain groups that may, or may not leave you a message.