We recently migrated from Slack to Mattermost. We are now facing the problem that a bunch of apps that we use (and have no control over) integrate exclusively with Slack. For example, Invision.
What is the best way to get these integrations onto Mattermost? I tried setting up a Slack relay, using Matterbridge to forward everything posted by Invision. However, formatting is mostly lost and the resulting messages are fairly useless.
Is there any generic way to get the messages of integrations and bots posting onto Slack verbatim into Mattermost? Or some other way to handle the Slack integration problem?
Unfortunately I’m not aware that we have a way to migrate Slack integrations to Mattermost, unless they use webhooks and slash commands which are Slack-compatible. One way would be Matterbridge but it seems that you have already discovered it and it wasn’t working properly. Here’s more details on what Slack migration supports: https://docs.mattermost.com/administration/migrating.html#migrating-from-slack.