Cross-realm raids and mail are a work in progress
Posted Mar 1st 2010 8:00PM by Zach Yonzon

That said, it might take a while longer before Blizzard implements cross-realm raiding although they said that they were looking into it. Aside from considerable technical issues, the developers were also concerned about group dynamics, such as how to get groups back together through those long raids that require more than one session. Another concern was keeping the sense of community alive in native realms. On the other hand, the growing culture of PUGs that has bloomed through easier content and the new Dungeon Finder has already diluted the sense of community in individual realms, so we should probably expect Blizzard to allow cross-realm cooperation sooner rather than later.
