Actors should be taking their own notes during rehearsals. I don't think it's the SM's job to pass notes from director to actor... then the actors will just get lazy and not take notes, because they know an email is coming that has all the information so why bother writing it themselves? It's important for me to know it, but it's not my job to know it FOR the actor.
I think it's a good idea for the SM to TAKE notes particularly in tablework, just record whatever ideas are spouted out... so that you have a resource to look back to, when somebody says "ok now what did we decide I was doing on this line?" or "go back to the way you were doing it before" etc. But those notes don't need to be emailed to the actors. Actors should be recording all notes that are given to them by the director, whether it's in rehearsal or, occasionally, via email (on those nights when you run out of time to give notes in rehearsal).
The only time I think it's acceptable to email notes to an actor is, for instance, last night was Q2Q. One of my actors called me saying "I'm on my way to rehearsal but I just brought my child to the hospital..." so as soon as he arrived we excused from rehearsal to go back and be with his family. We ran Q2Q and I took an individual set of notes for that actor - "make sure you arrive at your place by this line!" or the director calling out "hey [Actor] is going to have to wait for the sound to run before he speaks," but this was a really unique circumstance and it's absolutely not something I would do just for your everyday rehearsal. I'm definitely not going to just record everything the director says to the actors' faces and then send a copy of that to the actors...
I have been in situations where my director has typed up notes from a rehearsal, and sent them to me to ask me to distribute them to the cast, for consistency's sake... but in those situations it was made very clear that the notes were coming from the director and the actors should respond to her with questions, not me.
I do sometimes email performance notes, if the nature of the show is not conducive to giving face-to-face notes. So I'll email notes such as runtime, significant flubs, "this one scene was dragging a lot more than usual," "there was a traffic jam during a scene change, we're going to run it at call tomorrow," "your facial scruff is getting to be too much, please shave for tomorrow's show," etc.