As an end user, I want the WAYF/DS to list my IdP when I enter my email address

[FlorisFokkinga]

Use case

We might not have statistics, but I suspect it happens often that users enter their username (often their email address) at the WAYF, while they should enter a search term for their institution's IdP. We would like to list the user's IdP when they enter their email address.

Details

I suspect email address are easy to recogninize by the '@' and that the current search terms use the '@ ' symbol little.
It's fine if this works for most email addresses, based on the currently known IdP domains.