We have implemented offline group messages and offline IM received from hypergrid visitors. While the latter isn't perfect, it's the best we can do within the present OpenSim software. The main restriction is that you can't reply unless you teleport to the visitor's grid. Also, port information isn't available since this patch, so we have given you the best advice that we can in the email that you'll get if you receive such an offline email from a hypergrid visitor. The patch was well-intentioned and did not anticipate this side-effect.