Gregory's Server
#FediTips (or perhaps #FediWarnings?):
Something I discovered the other day on accident is in Mastodon and derivative software, if you are sending someone a DM, and you spontaneously tag someone in the middle of the message, *that person now has read access to the DM in which they're mentioned*. This is a neat feature if you're using it on purpose but could be awkward if you're just trying to link an account and suddenly that account can see you talking about them…!
Apparently this is a Mastodon-unique behavior and was not part of how messages worked in the original ActivityPub. (I don't know if it works this way on independent Mastodon reimplementations such as Pleroma.)