This Mattermost plugin lets team administrators delete old messages from their channels based on their age. It provides two commands:
/channel_idreturns the channel id/delete_poststhis is the command that actually deletes the messages.
The delete command is currently only able to delete messages older than a specific number of days. Pull requests to enhance its functionality (e.g. to allow messages sent between two dates, or other duration formats) are welcome.