Proton mail will let you do wildcard email and it’s only $3-4 a month. If you need smtp support then you can just setup a hydroxide container.

You never have to leave Plex, Overseer is just grabbing the watchlist from you and your users and then adding a new entry in Radarr set to monitored for that movie.

Best sleeper feature is that it can monitor stuff you add to the watchlist and grab it for you when available. Perfect to pair with that discover feature they added to plex a while back.