Hey there.
I don't know if any other guild leaders or such have had this issue before, but here goes.
So I'm in an RP guild with a friend of mine, he's the leader I'm the co-leader and as for RP, we use mailboxes to transfer rewards, missions, guild information etc. But the thing is, sending messages one at a time to every member seems very bothersome. Plus, you have to wait a minute or two between messages(I guess it's their anti-spam system) which even bothers me more. So my suggestion - make a mailbox system that allows members of a guild to send a single mail to all of the members of the guild. We approach the mailbox, use it, and somewhere in the box, put a new tab or something saying "Guild".
Tell me what you think, I think this is a worthy suggestion.