Slackline is a Rocket.Chat App that allows users to receive private messages from a connected slack workspace (the RC built-in slackbot does not have access to direct messages and private groups) and also import their private message history.

To use this app the Rocket.Chat administrator must (I) must install this app in the RC instance, (II) create a Slack app in their workspace and (III) enter the Slack app API keys in the settings for this app.

1. Goto Create Slack App
2. Enter a name and select your workspace
3. Click OAuth & Permissions in the Sidebar, enable the following scopes users:read, groups:history, groups.write, groups.read, mpim:history, mpim:write, mpim:read , im:history, im:write and im:read and save.
4. Click Add new redirect URL. Enter the url for the oauth endpoint from the Slackline settings page in your Rocket.Chat instance, click add and save.
5. Click Event Subscriptions the Sidebar and enable Events
6. Enter the url for the slackevent endpoint from the Slackline settings page in your Rocket.Chat instance as request URL.
7. Subscribe to the message.groups, message.im and message.mpim events.
8. Click OAuth & Permissions in the Sidebar. Click install app to workspace.

These instructions are for individual users of the RC instance:

1. To use the app enter /slackline login anywhere.
2. Click the link, login to slack
3. Go to any private channel of which you want to import the message history and do /slackline import. This can take a few seconds, so don't worry if nothing happens at first.
4. Enter /slackline enable to receive future messages from any private group, that you are part of, or from direct message conversation. This works only slack to RC, not the other way round.

Caution Due to API restrictions the app cannot check if messages have already been imported. So before importing any private conversations, check that messages haven't been imported already (by somebody else in the conversation) or you will have a lot of duplicates. I am aware of this issue, but I can't fix it until the Rocket.Chat developers implement the according functions in the Rocket.Chat App Engine (which is still in a beta stage).