Hey Josh!
For digests you can limit this to 14 per second by setting this Discourse global to 420, as follows in your container build file:
DISCOURSE_MAX_DIGESTS_ENQUEUED_PER_30_MINS_PER_SITE: 420
This is not “exactly” what you want but it is darn close.
Since 14 per second (from your post) times 30 seconds = 420, this global setting will limit digests to around 420 per every 30 minutes, just like the code “says”:
See also:
https://github.com/discourse/discourse/blob/master/app/jobs/scheduled/enqueue_digest_emails.rb#L37
Naturally, if your SMTP channel is sending other emails, you will need to adjust this down; or you can set up a different, separate channel for digest emails (like we do).
Note: This global setting is set to 10,000 per 30 minutes by default; which is a lot of digests per hour if you ask me ;). So, we set this much lower so we have a “reasonable” SendGrid bill each month.
30 digests per 30 minutes = 1440 per day, or around 43,200 per month (because we were sending a lot of digests before I made this change a few days ago). Next month, I will bump this up to around 60 digests per 30 minutes, or around 86,400 digests per month plus or minus.
Hope this helps.