All activity on calendar events someone subscribes me (or a project I'm in) to results in an e-mail notification.
Email preferences at https://phabricator.wikimedia.org/settings/panel/emailpreferences/:
Audits [ ⚪ Ignore ] A commit is created. [ ◐ Notify ] A commit has a concerned raised against it. [ ⚪ Ignore ] A commit is accepted. [ ⚪ Ignore ] A commit has an auditor resign. [ ⚪ Ignore ] A commit is closed. [ ⚪ Ignore ] A commit has auditors added. [ ⚪ Ignore ] A commit's subscribers change. [ ⚪ Ignore ] A commit's projects change. [ ◐ Notify ] Someone comments on a commit. [ ◐ Notify ] Other commit activity not listed above occurs. Calendar [ ⚪ Ignore ] An event's name, status, invite list, icon, and description changes. [ ⚪ Ignore ] An event's start and end date and cancellation status changes. [ ⚪ Ignore ] Other event activity not listed above occurs. Differential Revisions [ ◐ Notify ] A revision is created. [ ⚪ Ignore ] A revision is updated. [ ◐ Notify ] Someone comments on a revision. [ ◐ Notify ] A revision is closed. [ ◐ Notify ] A revision's reviewers change. [ ⚪ Ignore ] A revision's CCs change. [ ◐ Notify ] Other revision activity not listed above occurs. Maniphest Tasks [ ⚫ Email ] A task's status changes. [ ⚪ Ignore ] A task's owner changes. [ ⚪ Ignore ] A task's priority changes. [ ⚪ Ignore ] A task's subscribers change. [ ⚪ Ignore ] A task's associated projects change. [ ⚪ Ignore ] One of the tasks a task is blocked by changes status. [ ⚪ Ignore ] A task is moved between columns on a workboard. [ ⚫ Email ] Someone comments on a task. [ ⚪ Ignore ] Other task activity not listed above occurs. Pastes [ ◐ Notify ] Paste title, language or text changes. [ ◐ Notify ] Someone comments on a paste. [ ◐ Notify ] Other paste activity not listed above occurs. Phame Blogs [ ◐ Notify ] A blog's details change. [ ◐ Notify ] A blog's subscribers change. [ ◐ Notify ] Other blog activity not listed above occurs. Phame Posts [ ◐ Notify ] A post's content changes. [ ◐ Notify ] A post's subscribers change. [ ◐ Notify ] Someone comments on a post. [ ◐ Notify ] Other post activity not listed above occurs. Pholio Mocks [ ⚪ Ignore ] A mock's status changes. [ ⚪ Ignore ] Someone comments on a mock. [ ⚪ Ignore ] Mock images or descriptions change. [ ⚪ Ignore ] Other mock activity not listed above occurs. Projects [ ⚪ Ignore ] Project name, hashtags, icon, image, or color changes. [ ⚪ Ignore ] Project membership changes. [ ⚪ Ignore ] Project watcher list changes. [ ⚪ Ignore ] Other project activity not listed above occurs. Slowvote [ ◐ Notify ] Someone changes the poll details. [ ◐ Notify ] Someone votes on a poll. [ ◐ Notify ] Other poll activity not listed above occurs.
It would appear the values from the Calendar section are ignored.