Shared Mailbox vs. Distribution List vs. Group Inbox: Which Should You Use?

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Every business eventually needs a team email address. Info@, support@, billing@, hr@ — these functional addresses are how organizations receive email that doesn't belong to a single person. In Microsoft 365, you have three fundamentally different ways to create them, and choosing the wrong one creates practical problems that compound over time: users getting duplicate email, replies going to the wrong place, no shared history of who responded to what, or worse — paying for licenses you didn't need to buy.

This guide cuts through the confusion by explaining what each option actually is at the technical level, the licensing implications that affect your monthly bill, the right use case for each, and how to manage them from the Exchange Admin Center.

The Three Options at a Glance

Shared Mailboxes: The Right Tool for Most Functional Addresses

A shared mailbox is a real Exchange Online mailbox — it has its own inbox, sent items, deleted items, calendar, and contacts — but instead of being assigned to a single user, multiple users are granted access to it. Users open it as an additional mailbox in Outlook or Outlook Web Access alongside their own personal mailbox. When they send from the shared mailbox, the message appears to come from the shared address ([email protected]), not from their personal address.

The licensing reality: A shared mailbox under 50 GB of storage does not require a Microsoft 365 license. Users access it using their own licensed accounts — the shared mailbox itself is license-free. This is one of the most underutilized cost savings in M365. Many organizations have been incorrectly purchasing paid licenses for their info@, billing@, and support@ addresses when those addresses should have been shared mailboxes all along.

Once a shared mailbox exceeds 50 GB, it requires an Exchange Online Plan 1 license to expand to 100 GB, or an Exchange Online Plan 2 license for unlimited archiving. For most functional inboxes, 50 GB is ample for years of operation.

The shared sent items behavior: By default in Exchange Online, when a delegate sends from a shared mailbox, a copy of the sent message is stored in the delegate's personal Sent Items folder, not in the shared mailbox's Sent Items. This creates a problem: other team members opening the shared mailbox can see received messages but cannot see what was replied to, or by whom. The fix requires enabling the MessageCopyForSentAsEnabled and MessageCopyForSendOnBehalfEnabled settings via PowerShell or Exchange Admin Center — this is a configuration step that is often missed during initial setup and creates significant operational confusion on support teams.

Best use cases for shared mailboxes: info@, support@, billing@, hr@, reception@, any functional address where a team needs to collaboratively manage an inbox, track responses, and maintain a shared history of communications. Shared mailboxes are also appropriate for role-based addresses that need a calendar (a shared meeting room email, a department booking address).

Distribution Lists: Simple Broadcast Aliases

A distribution list (DL) is not a mailbox. It is an email alias that, when messaged, delivers copies of the message to each member's individual mailbox. Think of it as a broadcast mechanism. The DL itself stores nothing — there is no shared inbox, no shared sent items, no shared history. Each member receives their own copy of the email in their personal inbox.

This distinction has important practical implications. When a customer emails support@ configured as a distribution list, every member of the support team gets a copy in their personal inbox. When one team member replies, their reply comes from their personal address — the customer's reply thread is now in their personal inbox only. The other team members have no visibility into whether or how it was handled. There is no shared audit trail. For a collaborative support or customer-facing workflow, this is the wrong tool.

Distribution lists do not require licenses — not for the list itself, not for membership. Any licensed user (or even unlicensed external contact) can be a member.

Best use cases for distribution lists: Broadcast communication where replies are not expected or where each member independently handles their copy. All-staff announcements (allstaff@, everyone@), alert notifications from monitoring systems, newsletter distribution, bulk-send addresses where the intent is delivery to individuals rather than shared management of a team inbox. Also appropriate for announcements@ or newsalerts@ where the sender wants to reach everyone and no collaborative response is needed.

Microsoft 365 Groups: Collaboration Beyond Email

A Microsoft 365 Group (not to be confused with a security group or a distribution group) is a collaboration object that bundles together a shared mailbox, a SharePoint document library, a shared OneNote notebook, a Planner board, and optionally a Microsoft Teams workspace. It is the underlying infrastructure that powers Teams channels — when you create a Team in Microsoft Teams, a Microsoft 365 Group is created behind the scenes.

The M365 Group inbox functions similarly to a shared mailbox: messages sent to the group address arrive in a shared inbox that all members can read and reply to. However, the user experience is different — members can choose to have messages delivered to their personal inbox (subscribe) or just view them through the group interface. Replies from the group go through the group email address.

The licensing implication: Microsoft 365 Groups require that members have active Microsoft 365 licenses (Business Basic, Standard, or Premium at minimum). You cannot add unlicensed users as members of an M365 Group in any meaningful capacity. This makes M365 Groups unsuitable as a replacement for shared mailboxes or DLs in cost-optimization scenarios.

Best use cases for M365 Groups: Active project teams that need email plus file collaboration (a project folder in SharePoint, a shared notebook, task management in Planner), department hubs where the team already works in Teams and wants email as one channel among several, and any scenario where the team needs to collaborate on files and tasks alongside shared email. The group email becomes one communication channel within a broader collaboration workspace rather than a standalone inbox.

Management in Exchange Admin Center

All three object types are managed through the Exchange Admin Center (EAC) at admin.exchange.microsoft.com, though M365 Groups can also be managed through the Microsoft 365 Admin Center.

To create a shared mailbox: EAC → Recipients → Mailboxes → Add shared mailbox. After creation, add members under the Delegation tab by granting Full Access (allows opening the mailbox) and Send As (allows sending from the address). Grant both permissions for a functional team inbox — Full Access alone does not allow sending.

To create a distribution list: EAC → Recipients → Groups → Add group → Distribution. Add members and configure whether external senders can email the list (by default, only internal senders can). To allow external senders to email a DL (for a public info@ or contact@ that you want customers to reach), set the group to allow messages from "All senders."

To create an M365 Group: Microsoft 365 Admin Center → Groups → Active groups → Add a group → Microsoft 365. The group creation wizard walks through naming, privacy settings (public vs. private), Teams enablement, and initial member assignment.

Mobile Access to Shared Mailboxes

Accessing a shared mailbox on mobile requires a few additional steps that are not always obvious. On iOS and Android using the Outlook mobile app, users must be granted Full Access to the shared mailbox (same as desktop), then add the shared mailbox as an additional account in the app. In Outlook Mobile, go to Settings → Add Account → Add a Shared Mailbox. The app uses the user's credentials but opens the shared mailbox as a separate account.

How IT Center Manages M365 Mailbox Architecture

IT Center configures and manages Microsoft 365 mailbox infrastructure — including shared mailboxes, distribution lists, M365 Groups, and the associated permissions and policies — as part of our Microsoft 365 services. We regularly audit existing M365 environments and find unnecessary paid licenses assigned to shared mailboxes, distribution lists configured where shared mailboxes belong, and missing sent-items synchronization settings that leave support teams without response history. We also configure mobile access, Outlook delegation, and email security policies for shared mailbox environments.