IMs -
I am not banning IM RP. It is useful for side conversations that would otherwise eat up a lot of game time with 5/6 players on the sidelines. However, the rule is that IM RP is only to be for these side conversations, it is not to take place when other PCs are in earshot of the conversation and/or would have reason to join in the conversation (or listen in). If all the PCs in earshot are part of the IM conversation (or were offered to be part of the IM convo and didn't want to, not didn't have time to), this does not apply. If it is a conversation between two PCs, please send a transcript of the convo to the GM so there is not XP docked later for mistakenly believing you are metagaming.
Message Board RP -
Is going to more or less be for bookkeeping purposes only. Posting a list of rumors your character overheard, letters to other characters, or other non-interactive bits. It can also be used to sum up your character's activities while shopping or doing some sort of non-party action.