We all have our own preference on which free email to sign up with and a lot of it will boil down to ease of use. Yahoo, Hotmail and Gmail are leading the pack but as far as user-friendliness is concerned, a lot has to go with where we feel comfortable with at the most.
These mails sites normally try to copy each other. They offer beta versions of new releases which do not always become ideal for people today. Take Yahoo for example which is trying to copy Gmail. It is commendable but the loading time is really something that leaves a lot to be desired.
Hence it would be best to stick to old scripts for now. Do not offer beta versions if they create more inconveniences for your patrons.