It is now very much the exception rather than the norm that a report will be acknowledged by e-mail.
Here is the opening post from the thread announcing the change:
RebeccaMumsnet (MNHQ) Wed 13-Jul-16 11:52:08
Hi all,
As you know, we rely on MNers to use the 'report' link if they spot anything untoward on the boards - and we very much appreciate it when you do. We want to be able to be more responsive to these reports generally, so we're going to stop sending individual acknowledgment mails for now; we think this will free up a fair bit of time which could be better spent elsewhere.
When you report a post, you'll now see this message:
Thanks very much for reporting this - we rely on your reports to make sure Mumsnet is a brilliant place to come for support and advice.
In order to best focus our efforts, we tend not to respond to reports individually - but be assured that we read every single one, and that we'll look into the problem as soon as possible.
And we'll be highlighting a few links to places you might want to go next.
We'll continue to mail folks directly as and when the need arises - and as mentioned, we'll be reading each and every report, come what may. In the meantime, if you have any questions, please do ask!