feat: implement phantom_threading to group email alerts into threads #4623
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Some email clients such as Gmail apparently use their own heuristics for threading and already implement this behavior based on the subject. But for users of other email clients that only implement threading based on the relevant headers (e.g. notmuch), those users currently get one email thread for each newly firing alert. With phantom_threading enabled, all alert emails (of the same alert) on the same day are grouped into the same thread. Much nicer :) Signed-off-by: Michael Stapelberg <stapelberg@google.com>
sysadmind
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Oct 24, 2025
| if n.conf.PhantomThreading && len(as) > 0 { | ||
| // Add threading headers. All notifications for the same alert | ||
| // (identified by fingerprint) on the same day are threaded together. | ||
| // The thread root ID is a phantom Message-ID that doesn't correspond to |
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I assume this is where the name "Phantom Threading" comes from? I'm not sure people will understand that based on the name. Maybe "daily threading" would make more sense, although in that case what if we want to do a different threading strategy in the future?
| } | ||
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| // Use first alert as representative of the alert group. | ||
| alert := alerts[0] |
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Doesn't that mean even if we have 30 alerts, whatever the first one is, that's what will be used for fingerprinting? What if that alert resolves, but the other 29 remain?
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Some email clients such as Gmail apparently use their own heuristics for threading and already implement this behavior based on the subject.
But for users of other email clients that only implement threading based on the relevant headers (e.g. notmuch), those users currently get one email thread for each newly firing alert.
With phantom_threading enabled, all alert emails (of the same alert) on the same day are grouped into the same thread. Much nicer :)
I have tested this manually and you can see the effect start to work in this screenshot:
(Monday morning, I got one thread per alert email notification; in the evening, the threading change was effective and emails are grouped into the daily thread.)