Reach
The sender sets a priority. You set, per source, how far a notification is allowed to reach. Reach is a ceiling; priority only moves down from it.
The four levels
Reach
Reads as
What happens
Silent
Inbox only
Lands in the inbox and nowhere else. No sound, no banner, no badge, and nothing leaves the app: email, Slack and webhooks never see it.
Badge
Inbox · icon badge
The app icon's count goes up. No sound, no banner. On iPhone a passive notification; on Android a low-importance channel.
Banner
Banner · sound · held in Focus
A banner and the sound. On iPhone an active notification, so a Focus holds it; on Android the default channel.
Break through
Banner · sound · also in Focus
A banner and the sound that also shows inside a Focus and the scheduled summary. On iPhone a time-sensitive notification; on Android a high-importance channel. Email gets Now: in the subject; Slack gets @here.
A new source starts at Banner. Change it on the source's page, and everything it sends from then on follows.
How priority meets it
The effective reach is the lower of the source's Reach and the priority's own level, where low maps to Badge, normal to Banner, and high and critical to Break through.
low
Badge at most. Never sounds, always groups.
normal
The source's Reach as it is. The default when a sender says nothing.
high
Break through at most. Never grouped away; pinned to the top of the inbox for 60 minutes.
critical
Break through at most. Never groups; may pass quiet hours and Focus when the source's switch and the account's master switch are both on.
So a source held at Badge can never sound, whatever its script says, and a source at Break through still lets a low notification stay quiet.
On each device
On the iPhone every source is its own thread, the source's icon is the avatar on the lock screen, and the sound is the account's or the source's own. On Android there is one channel per Reach level, created at first run, so the system's own notification settings stay in charge. In a browser, Badge and above show a notification; Silent stays in the tab. Email and Slack send Badge, Banner and Break through, never Silent.
Next
Quiet hours · Grouping · Payload reference