Groups
A group equates a single mail address to a list of mail addresses.

For example:

A group with the address sales@mailenable.com.au could contain an array of other addresses. If anyone sends a message to the groups address, the message is automatically delivered to all the members of the group. People can only become a member of a group if the Mail Administrator adds them as a member.

Lists
A list also provides the above functionality, however there is more control over how messages are published and how people become a member of a list. The most significant difference is that people can subscribe to a list via e-mail. They send a message to the lists SMTP address with the keyword 'subscribe' in the subject (they can also unsubscribe by placing unsubscribe in the subject). It is possible to moderate a list, forcing all messages sent to the list to be routed to a moderators address. Only the moderator can publish to the list. Any messages sent to the list by the moderator are immediately distributed to the subscribers of the list.

Another option when using the list server, is the ability to configure a list that will send out a confirmation code for any user wanting to subscribe to the list, thus requiring the user to reply back to the list using the confirmation code to successfully subscibe to the list.

Additional extensions available to lists are outlined in the MailEnable Professional Edition documentation.