Universal Limit for Emails/Time

Is there a way to cap the total emails per unit time that the forum can send?

I got myself into trouble by making a tag ‘watch by default’ and then applying it to a post, which sent an email to thousands of users in the span of 20 minutes and got my email account suspended (several users’ email addresses had gone stale).

There are number of ways I could have avoided that, but to be sure I remain on good terms with my email provider, I’m looking for a way to enforce a slowdown when something would result in too many emails going out in a short span of time (provider would like assurances that it will never exceed 400/hr).

Anything I can do? I’ve seen other threads but nothing recent, and consensus seemed to be changing e.g. max emails per user per day, but none of them address the situation where every user gets 1 email.