Is it possible in Discourse for an admin to send a digest in bulk to specific users or email addresses whenever they want?
No, digest emails are sent automatically. There are some site settings that you can change to adjust when they’re sent, like Default email digest frequency but note that users can always opt-out of digests entirely from their preferences.
Sort-of. You can visit /admin/email/preview-digest and preview what people will see as well as change their last-seen date to see what the digest messages look like. You can then send that summary to any email address you want.
But you can’t do it in bulk, and those messages already go out automatically, so you’d just be sending them another one.
What problem are you trying to solve?