I notice that Digests are sent in batches together to a lot of users at once. I’m curious if it would be possible to have those spread out more so that you’re not causing a big sudden spike of traffic from the Digests being sent. I notice from my MailChimp stats from campaigns that go out, people seem to open/click emails by a huge margin in those first few hours after an email goes out, if they’re going to at all. So spreading out the Digest emails in Discourse could help. I have over-provisioned with the DigitalOcean droplet I have, so it’s not a big deal for me - but might be helpful for those that are just on the edges of hardware for their Discourse.
We should add some random variation to when we send these out. But it seems unlikely you would have perf problems from even a few hundred people clicking through. And people don’t always read their email at the same time.
Most email opens happen soon after a campaign is sent: http://www.quora.com/On-average-how-soon-is-an-email-opened-by-the-recipient-after-it-is-sent