This drives me insane. Lazy input boxes that only accept email domains from the big names.
My pet hate is my bank refusing to email me bank statement notifications to mail@mydomain.com ("not a personal address"), yet their password validation and marketing emails get through quite OK. Somehow they seem incapable of acknowledging that one department of the bank has made a technical decision in conflict with other departments...
Yes. But like most forms of discrimination, it's probably 100% legal. Same as Chuck's Pizza Parlor refusing to deliver outside an X mile radius, and 1st National Bank refusing to use the full legal name of anyone who's name exceeds the size of their DB's 'CustomerName' field.