I’m sure every email platform and every messaging expert will have slightly different definitions for these kinds of groups, but this is more-or-less the way that these terms are used in Microsoft-Land.

Contact Group – A group of contacts stored in a contact folder in a single mailbox and usable only by people with access to that mailbox folder. Ideal for contact groups that would only ever be used by one person.

Distribution Group – Also known as a Distribution List. A group of contacts stored in Exchange and usually available in the Global Address List. May only contain recipients from the organization’s internal Global Address List (aka GAL, Global Address Book or Offline Address Book). Distribution groups are usually managed by group owners, but they can be configured to allow members to join and leave the group without admin approval.

Dynamic Distribution Group – An Exchange distribution group stored in Exchange and automatically populated by a formula (an LDAP query) based on properties of existing recipients in the Global Address List, such as department name or a custom attribute field. Dynamic groups don’t have membership lists. Membership is determined by the underlying LDAP query as each message is received and sent to all recipients who match the query.

Microsoft 365 Group – An Exchange Online group that uses a subscription-based model to determine if members see messages only in the group mailbox or also in their own Inbox. Can contain both internal and external members, regardless of whether they appear in the Global Address List. Microsoft 365 Groups include a SharePoint site to facilitate document sharing and are used by Microsoft Teams to manage Team and Private Channel membership.

Listserv – A subscription-based discussion group that can contain any recipient and can be used like a distribution group. Members can usually modify their subscription to receive a copy of every message sent to the group, a daily or weekly digest of messages, or to read messages only by logging into a website. Listserv groups are not supported in Exchange, but they share some common features with Microsoft 365 Groups. The term LISTSERV technically refers to a product offered by L-Soft, it is often used as a catch-all term for all kinds of email groups and lists, much like “Coke” is used to refer to all carbonated soft drinks and “Xerox” to refer to all photocopying devices, regardless of the actual manufacturer.