Share Group across email apps


New Email
We have a club, all volunteers. We send out several emails a week. We edit the group file several times a month (new members, deleted members, edits). One person has been doing this using Hotmail and would like to "share" the task with some other members. Those who have "volunteered" use Gmail and MacMail. Is there any easy way to ensure that everyone is using the most current Group list across the various apps?