Stream suddenly sent tons of alerts based on hidden post type, possibly due to REST API change in 3.9.0

[cbirdsong]

Yesterday one of our sites suddenly started sending tons of Stream alert emails about deleted items. It had this alert configured:

This site has Post SMTP plugin installed with logging enabled. It uses a hidden postman_sent_mail custom post type for logged items, and it limits the log size by is a fixed number of posts, instead of a time period like Stream:

Stream's records show "item deleted" alerts being sent after Post SMTP sends and logs an email, which creates a new postman_sent_mail and presumably also deletes the oldest one: stream-filtered-redacted.csv

This seems like it could be a consequence of monitoring REST API changes (#1264), so it might be good if alert monitoring only applies to public post types by default?

[kasparsd]

Thanks for the detailed report @cbirdsong! Can you please confirm if this is happening when new postman_sent_mail posts are created and deleted as the Post SMTP plugin schedules and sends emails?

[cbirdsong]

I disabled the alert as soon as I discovered it and didn't attempt to debug by triggering any further emails since it was on a live site, but the times in the Post SMTP log lined up exactly with the Stream log/emails.