A few users contacted me on the weekend to complain they were being inundated with emails telling them there were new posts on topics they were interested in. But when they went to check, there was nothing new there. 

So why did it happen? As I suspected, it was a glitch at Boardhost. 

To their credit, they responded to an email from me asking for an explanation. Here it is:

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Hi,

What's going on is that our mail server decided, without consulting anyone, to die unexpectedly. While it was taking its unscheduled vacation, roughly two weeks' worth of email notifications quietly piled up in a queue.

Once the issue was fixed, the server enthusiastically set about delivering everything it had been holding onto. As a result, users have been receiving notifications for messages, requests, and other events that may already have been dealt with, expired, or otherwise ceased to be exciting news.

The good news is that the problem has now been resolved and the backlog has been cleared. The bad news is that there isn't a way to selectively make only the emails people wanted arrive while suppressing the ones they didn't. Things should now be back to normal, and no further delayed notifications should be generated.

Thank you,

Boardhost Support
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So apologies to those who got too much mail from them and me. It shouldn't happen again!