There are some additional reports of this in Faire Grounds here: https://www.tarvalon.net/index.php?threads/competition-day-1-community-engagement-the-longest-chain.45048/#post-1729502 @Serinia Edoras @Tallan Daar @Erin al'Denael
As far as I'm aware, there's not a setting that will send emails for @ mentions. You can receive an alert on the boards (settings managed under Alert Preferences), but not an email.
Someone in tech can correct me if I'm wrong though, but I don't see anything for it.