Getpubkey request on chan does not get a response from subscribers, however since mailchuck does send messages to chans, someone must have set it up as a normal address. It needs to be investigated if there are issues with this. A subscriber, when posting to a chan, ignores the pubkey objects though (I investigated this when I was looking for a way to increase chan difficulty, and there currently isn't a way for channel subscribers to synchronise what difficulty the chan should have).