Acknowledge vs Noted

Solution 1:

You could certainly use acknowledged. You need the past tense form.

"Acknowledge" in the present tense will look like a command to the person who receives the email, not as a response.

In general, I find if you only say this, it will sound a bit terse and could be taken as rude.

Generally, I prefer less formal responses like your example or "OK, got it", "Thanks, I'll make a note of that".

Solution 2:

There are two words in the lingo of aviation radio communication, "roger" and "wilco." The first (named after the name of the letter "R" in the old radio alphabet) stands for "I received your transmission." "Willco" is short for "I have received your transmission and will comply with your order." When your friend replies to a message by saying "acknowledged," it sounds like he means "roger." If that message is a request or a command, the sender is not only interested in hearing that the message has been received, but he also wants to know whether the request will be honored or the command obeyed. "Roger" and "acknowledged" don't give that assurance. To avoid confusion in that instance, your friend should find some locution that means wilco.