I’m not really that deep into Boards as of yet, I wasn’t aware that you can “subscribe” a board to a channel.
How did you do that? I just clicked around a bit and did not find an option to do that.
Are you referring to the “Follow” Feature on cards (Work with cards — Mattermost documentation)?
I’m not 100% sure if an update posted by a bot in a channel will trigger an outgoing webhook, but as soon as I know how to set up a board subscription to a channel, I’ll give it a try 