This idea is designed for the professional meeting goers out there as well as those who's colleagues think they should be answering emails rather than getting on with their normal work.
Its just a simple "policy" to treat emails like a sms response. Short a precise without any unnecessary fluff.
Of course its a good idea to open politely and not use any text slang. Having a automatic footer signing off as well doesn't hurt either but essentially keeping the word count to a minimal to get through emails as quick as possible.
three.sentenc.es is a personal policy that all email responses regardless of recipient or subject will be three sentences or less. It’s that simple.