@fmarier I have come across this too, and find it a worrying sign. I am not sure I want to deal with an organisation which is so ignorant of the internet that they think they are helping their users by having a box to enter your username and a dropdown for whether you are (gmail.com, outlook.com, live.com ... - I think there were less than 10).
Almost as alarming to find the number of Universities - who should know better - running their email on MS Exchange.