New invitees are complaining they need a yahoo e-mail account to obtain access to the group, is it required?

I understand it is 'yahoo groups', but new invitees complain they need a yahoo e-mail account to obtain access to the group webpage. In the past you could have any account to get access to our site to view the calendar or download files posted by the moderators. Has anyone discovered to 'toggle' of the yahoo sign in? Unfortunately 60% of my members use their work e-mail address.