When you have multiple devices, for example an iPhone, iPad and macOS, reading a notification / message on 1 device, should also remove the notification (“read status”) on all other devices.
When reading a message on 1 device (for example the iPhone), the other devices will still display the unread notification, until you’ve manually launched the app.
Thank you!
It already works like this on Desktop and Android if the application is connected to the server and can notice that the message was read. On iOS dismissing the notification requires waking up the application using a push notification over Apple servers, and no such notification is sent currently even by chatmail servers.
There is however a plan to replace current method of setting IMAP \Seen flag with sending a read receipt to self: Send MDNs to self · Issue #7005 · chatmail/core · GitHub. If receiving such read receipt will trigger a push notification, iOS application will have a chance to dismiss the notification.