Also do I have to add the @domain.com in my web email login or does it know because it's a hosted service? As a user I'm confused.
If it's a single-domain hosted email provider, a well-designed system would accept either the local part or the full email address, but using the full email address would avoid problems in the future in case the service expands to a second domain.
The local part of an email address is not an email address. If it asks for an email address during login, assume it means an email address.
A trend that I just adore is letting people log in with either username or email on the same form, so it doesn't matter.
Umm it starts with a placeholder so you know if it's user name or email. If you get it wrong an error is displayed. Kind of hard to mess up a login form.