In Slack (at least in their Mac app)1, you can click on the x button on the left side of an inline media (unfurled attachment) and close it.
When you do so, Slack shows a dialog and asks you if "Are you sure you wish to remove this attachment from the message?" and there is an checkbox that gives you the option to "Disable future attachments from this website?".
I checked that box an permanently disabled expansion of media from a certain domain. But now I want them back, but cannot find a way to do so.
So basically, I want to re-enable expansion of inline media for URLs from a domain I disabled through that dialog.
1 It is not a native client problem. The same story holds for the web client or the Mac or iOS clients. I actually tried them all.
Best Answer
You will find the list of blacklisted links in the Admin Settings > Attachments tab.