Steam's protocol in Go to allow automation of different actions on the Steam network without running an actual Steam client. Includes APIs for friends, chatting, trading, trade offers and TF2 crafting.
If you wanted to retrieve the Steam client's email domain (gmail.com), you had to sucessfully login to Steam and access it with the LoggedOnEvent. Now you will be able to access the client's email domain from a LogOnFailedEvent.
With the SteamKit2, you are able to access the EmailDomain before a successful logon. This is so you can prompt the user to check their email at gmail.com (or their own email domain).
If you wanted to retrieve the Steam client's email domain (gmail.com), you had to sucessfully login to Steam and access it with the LoggedOnEvent. Now you will be able to access the client's email domain from a LogOnFailedEvent. With the SteamKit2, you are able to access the EmailDomain before a successful logon. This is so you can prompt the user to check their email at gmail.com (or their own email domain).