At the library where I work sometimes things are done the wrong way. And sometimes when that happens someone, often a manager, will complain "But I sent an email about this!".
Informational emails are great. They are important. I fully endorse their use.
But they are not 100 percent immediately effective. Rather they are like vaccines. Indeed, they are exactly like vaccines.
Like a vaccine any informational email will have an effectiveness rate depending on the subject and quality of the email. This will depend upon a combination of the clarity and sensibility of the issue of the email, how well written the email is, and how many people actually read their email. This can make one of these emails anywhere from 20% to 95% effective.
Like a vaccine most informational emails are safe. But they may have minor side effects like irritation or soreness around the site of the email (like, "I can't believe I'm getting another stupid email about this issue. I already know this!"). Sometimes there are also short term illnesses as the body builds up its resistance (like, "Ugh, we have to walk these all the way over there now! I'll just pile them up here for a bit first.").
In the end the ideal goal of any informational email is herd immunity, the state wherein the information of the email has been fully absorbed by the workplace. The path to this can be seen in the following scenario:
"Hey. That doesn't go there."
"There was an email."
"Oh. Was it that one I didn't read?"