Google calendar messages (meeting invites and updates, not meeting reminders) have the header

mailed-by:  calendar-server.bounces.google.com

Alas, filtering by mailedby:calendar-server.bounces.google.com or mailed-by:calendar-server.bounces.google.com does not work.

How can I filter the Google Calendar messages?

At this time I am using

subject:("Invitation:" OR "Canceled Event:" OR "Declined:" OR "Accepted:")

but this does not include meeting updates because their subject sometimes starts with [Update] and Gmail filters cannot handle brackets (even with backslashes &c - believe me, I know regexps).

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