Allow users to send individual posts without triggering notifications

Summary

Add a "Send silently" option for normal users when sending a message.

This would allow a user to send a message that is delivered normally, but does not trigger a desktop, mobile, or email notification for the recipient.

Motivation

There are many situations where I want to send someone a message immediately, but I don't want to disturb them.

For example:

• Sending a work-related message outside working hours
• Sending a message on a weekend or holiday
• Sending something late at night so I don't forget about it
• Sending several messages while knowing the recipient will read them later

Currently, the alternatives are either:

• Wait until an appropriate time to send the message
• Send it normally and potentially disturb the recipient
• Schedule the message, which isn't always appropriate when I want the message to be available immediately

A per-message "Send silently" option would solve this cleanly.

Existing support

Mattermost already has server-side support for silent posts. The current implementation allows bot accounts, OAuth apps, incoming webhooks, and plugins to create posts that are visible normally but don't produce notifications, unread badges, or the "New Messages" separator.

It would be great to expose this capability to normal users as well.

Proposed UX

Add an option to the Send button, for example:

Send ▼
  ├── Send
  └── Send silently

Or a keyboard shortcut could be provided as an alternative.

The message should otherwise behave like a normal message: it should be delivered immediately and remain visible in the conversation.

Example

I'm working on Saturday and remember something I need to tell a colleague.

Instead of:

"I'll send this on Monday."

or:

Send now → colleague receives a notification on Saturday

I could choose:

Send silently

The colleague would see the message normally when they next check Mattermost, without being disturbed at the time it was sent.

Expected behavior

When "Send silently" is selected:

• The message is delivered immediately.
• The message appears normally in the conversation.
• No desktop notification is generated.
• No mobile push notification is generated.
• No email notification is generated.
• The recipient's notification settings are otherwise unchanged.
• The sender can choose this independently for each message.

This should be a per-message choice rather than a change to the recipient's notification preferences.

Additional consideration

Since silent posts already exist for integrations, this feature could potentially reuse the existing server-side silent post mechanism rather than introducing a separate notification system.

The main product decision appears to be whether ordinary users should be permitted to use the existing capability and how it should be exposed in the UI.