For

• macOS (OS X) using terminal-notifier.
• Generic System which implements GNOME Desktop Notifications and has notify-send binary.
• Other system which implements notify-send binary/script.

Config

Below are ways to configure when or if this plugin should notify.

/set notify_priv <level>
/set notify_chan <level>

where notify_priv are private messages
where notify_chan are highlight messages in a channel
where <level> is one of:
    never  - never notify for these events
    active - never notify for these events if the channel/user is the active window
    always - anytime highlighed or private message, active window or not

Depends

macOS

The Following binaries should be findable in your $PATH.

terminal-notifier

Get with homebrew.

brew install terminal-notifier

other

The Following binaries should be findable in your $PATH.

notify-send

Get with your package manager, likely under some libnotify, notify-osd, package.