Eavesdropping through walls is something that has always skirted along the lines meta-gaming and power gaming. This has always been something that has been a grey area within the community.
It is common sense not to listen to and use information gained through walls. This is mainly because there is no possible way of telling wall density and implementing a system that could tell you density to use for personal gain, would be power gaming.
However, listening through areas such as clear glass (that
both sides can see through) and wooden doors are perfectly fine.
If you are also having a private conversation, we do also recommend setting your voice to whisper. You can do this by hitting Shift + H and setting the Voice HUD to W.
It’s common sense, which is why there isn’t even a rule for this in the first place.