Next channel or direct message in left hand sidebar with unread messages

`Alt` + `Shift` + `Down Arrow`

All hotkeys for Mattermost (MacOS)

Files Upload a file	`Command` + `U`
Navigation Shortcuts Previous channel or direct message in left hand sidebar	`Alt` + `Up Arrow`
Navigation Shortcuts Next channel or direct message in left hand sidebar	`Alt` + `Down Arrow`
Navigation Shortcuts Previous channel or direct message in left hand sidebar with unread messages	`Alt` + `Shift` + `Up Arrow`
Navigation Shortcuts Next channel or direct message in left hand sidebar with unread messages	`Alt` + `Shift` + `Down Arrow`
Navigation Shortcuts Open a quick channel switcher dialog	`Command` + `K`
Navigation Shortcuts Open account settings	`Command` + `Shift` + `A`
Navigation Shortcuts Open recent mentions	`Command` + `Shift` + `M`
Messages Shortcuts/Snippets Reprint previous message or slash command you entered	`Command` + `Up Arrow`
Messages Shortcuts/Snippets Reprint next message or slash command you entered	`Command` + `Down Arrow Arrow`
Messages Shortcuts/Snippets Edit your last message in the current channel	`Up Arrow`
Messages Shortcuts/Snippets Autocomplete @username beginning with character	`@ character` + `Tab`
Messages Shortcuts/Snippets Autocomplete channel beginning with character	`~ character` + `Tab`
Messages Shortcuts/Snippets Autocomplete emoji beginning with character	`: character` + `Tab`
Executing Commands Post a message as yourself, optionally adding a delay	/echo message `delay in seconds`
Executing Commands Join a channel	/join channel-name
Executing Commands Log out of Mattermost	/logout
Executing Commands Post a message as yourself in italics	/me message
Executing Commands Post a message as yourself followed by ¯\_(ツ)_/¯	/shrug
Executing Commands Send a direct message to a user	/msg @ `username` message
Executing Commands Collapse all link previews	/collapse
Executing Commands Expand all link previews	/expand
Executing Commands Send an email invitation to listed addresses	/invite_people `[email protected] ...`
Executing Commands Set your status away	/away
Executing Commands Set your status as offline	/offline
Executing Commands Set your status as online	/online
Executing Commands Displays a list of aII keyboard shortcuts	/shortcuts