Forum has stopped sending email notifications

phpBB has stopped sending me notifications of new posts on subscribed topics. Have I broken something? I’ve checked junk mail in Outlook and M365/Exchange online quarantine. Nothing there.

Already for quite a while…

Go to user control panel, tab subscriptions.
That’s how I keep track of responses in subscribed threads now.

Edit: ah wait … it starts working again ?
For how long ?

Hmm… bit intermittent. I received an email for your reply!

Yeah it’s definitely broken/intermittent.

They seem to have got a lot better recently, i.e. I’ve started receiving email notifications again.