- Guild Mail
- In-game mail sent between guild members now arrives instantly.
Guild Mail is a guild perk that makes mail between guild members arrive instantly.
Trivia
This perk's original name, "G-Mail", was likely a reference to Gmail, a popular email service from Google.
Patch changes
Patch 6.0.2 (2014-10-14): Guild level system removed; this perk is now granted to all guilds (instead of those at level 15). 
Patch 4.3.0 (2011-11-29): Renamed from "G-Mail". - Patch 4.0.3a (2010-11-23): Added.