Drop the Attitude, Keep the Message
When I was a supervisor, I often had technicians say this and other people in the office as well and really all over. So I'm gonna ask you to think about what this statement says as I said before, or like I told you earlier, or as per my email, please don't do that. I can't think of a more passive, aggressive insult.
Of course most people don't intend to do that, but if the person didn't get it the first time or the second time, what makes you think they're gonna get it the third time? So just restate the point. I know you probably know this, I have to say it and then review or summarize whatever it is you need to do.
If you need to send an email, don't put as per my last email, just state the point, get to the point and restate it. Sometimes you're just under the impression that the person received an email and they never got it. And there you are saying, like I said before, so please come across with curiosity, the intention to understand, not assign blame, to point out who's wrong and to win.
The last thing you want to do is start to build distance between you and your customers and your teammates, just because of the way you communicate, whether you have good intentions or not. So simply restate it. Ask the person to summarize if you think the person didn't get the message the first time.
Whether it's verbal or email, ask them if they got it. I'm just curious if you got our last email or, and our last conversation, I'm not sure if I stated this. So if I'm repeating myself, forgive me. And the person often will say, that's the first time I ever heard that. And it may be that they just don't remember that part of the conversation.
So approach it positively, frame it in a good way that's simple to understand and always seek a solution and make your customers collaborators. Don't increase conflict. I.