How to Set Up a Shared Mailbox in Microsoft 365

Shared mailboxes are one of the most useful and most misunderstood features in Microsoft 365. Every small business needs at least a few of them, whether it is info@, sales@, support@, or accounting@. They let multiple people read and respond to email from a single address without sharing a password and without paying for an extra license. But the setup process has enough options and gotchas that it is worth walking through properly rather than figuring it out by trial and error.

What a Shared Mailbox Actually Is

A shared mailbox is a mailbox that does not belong to any single person. It has its own email address and its own inbox, but no one logs into it directly with a username and password. Instead, you grant access to specific users, and the shared mailbox appears automatically in their Outlook alongside their personal mailbox. They can read incoming messages, reply to them, and send new messages from the shared address.

The key advantage is that no license is required for a shared mailbox as long as it stays under 50 GB. This makes shared mailboxes the right choice for any team email address, departmental inbox, or converted mailbox from a departed employee. Converting to a shared mailbox before removing the license is the standard way to preserve email access without ongoing cost.

Shared Mailbox vs Regular Mailbox vs Distribution List

Before creating a shared mailbox, make sure it is the right tool for what you need. These three options get confused constantly.

A regular (user) mailbox belongs to one person, requires a license, and is accessed with that person’s credentials. Use this for individual employees. Do not create a regular mailbox for a team address like info@ because it requires a license and someone has to “own” the login, which creates problems when that person leaves.

A distribution list forwards incoming email to a group of recipients. It does not have its own inbox. When someone emails the distribution list address, each member receives a copy in their own inbox. There is no shared view of what has been received or who has responded. Distribution lists are good for announcements and one-way communication but bad for collaborative email handling because there is no coordination between recipients.

A shared mailbox has its own inbox that multiple people can access. Everyone sees the same messages, can see whether someone has already replied, and can organize messages into folders. It is designed for collaborative email handling where multiple people need to manage incoming messages from a single address.

If you need a team email address where multiple people handle incoming messages, you want a shared mailbox. If you need to broadcast messages to a group of people, you want a distribution list. If you need a combination (a shared inbox that also receives messages sent to a group), you can mail-enable a Microsoft 365 Group, but that is a different setup with different behavior. For a detailed comparison of all four group types and when to use each, see Microsoft 365 Groups vs Distribution Lists vs Shared Mailboxes.

How to Create a Shared Mailbox

Step 1: Open the Admin Center

Go to admin.microsoft.com and sign in with an account that has Exchange admin or Global admin permissions. In the left navigation, go to Teams & groups > Shared mailboxes.

Step 2: Create the Mailbox

Click “Add a shared mailbox.” Enter the display name (what people see when they receive email from this address, like “Acme Support”) and the email address (the actual address, like [email protected]). Click “Save changes.”

The shared mailbox is created immediately. You do not need to assign a license. Microsoft provisions it automatically as a shared mailbox type that does not consume a paid license.

Step 3: Add Members

After creation, click on the shared mailbox and select “Members.” Add the users who should have access. Each member will see the shared mailbox appear in their Outlook automatically within an hour, though it can sometimes take up to 24 hours. Members can speed this up by closing and reopening Outlook.

Only add people who genuinely need access. Every member can read all messages and send from the shared address. There is no granular permission within the mailbox itself, so if someone should only see certain messages, a shared mailbox is not the right solution for that use case.

You can add and remove members at any time without affecting the mailbox contents or other members’ access. When an employee leaves the company, remove them from the shared mailbox as part of the offboarding process. When a new team member joins, add them and the mailbox appears in their Outlook automatically.

Step 4: Configure Send As vs Send on Behalf

There are two ways members can send email from a shared mailbox, and they look different to the recipient:

Send As means the email appears to come directly from the shared mailbox address. The recipient sees “From: [email protected]” with no indication of which team member actually sent it. This is the most common configuration for customer-facing shared mailboxes where you want a consistent sender identity.

Send on Behalf means the email shows both the shared mailbox and the individual sender. The recipient sees “From: John Smith on behalf of [email protected].” This is useful when you want recipients to know which specific person responded while still keeping the shared address visible.

To configure Send As permissions, go to the Exchange admin center (admin.exchange.microsoft.com), find the shared mailbox under Recipients > Mailboxes, open its properties, go to Delegation, and add users under “Send As.” By default, members only get Full Access and Send on Behalf. Send As must be explicitly granted.

Important Settings to Configure

Sent Items

By default, when a member sends email from a shared mailbox, the sent message is saved in the member’s personal Sent Items folder, not in the shared mailbox’s Sent Items. This is almost never what you want, because other team members cannot see what was sent.

To fix this, you need to configure the shared mailbox to copy sent items to its own Sent Items folder. This requires Exchange Online PowerShell:

Set-Mailbox [email protected] -MessageCopyForSentAsEnabled $true
Set-Mailbox [email protected] -MessageCopyForSendOnBehalfEnabled $true

Run both commands to cover both Send As and Send on Behalf scenarios. This is one of the most commonly missed settings when creating shared mailboxes, and it causes confusion when team members cannot find sent replies.

Auto-Replies (Out of Office)

Shared mailboxes can have their own auto-reply settings, separate from any individual member’s out-of-office. This is useful for setting expectations on response times. In Outlook on the web, open the shared mailbox, go to Settings > View all Outlook settings > Mail > Automatic replies, and configure the message.

Mailbox Size

Shared mailboxes get 50 GB of storage for free. If you need more than 50 GB, you must assign a license to the shared mailbox, at which point it has the same storage as a regular mailbox (50 GB with Exchange Online Plan 1, 100 GB with Plan 2). Most shared mailboxes will never reach 50 GB, but high-volume customer service mailboxes may need monitoring.

If the shared mailbox is approaching the limit, archive old messages or delete what is no longer needed before assigning a license. Paying for a license just because nobody cleaned up old email is an avoidable cost.

Permissions for External Senders

By default, anyone (internal or external) can send email to a shared mailbox address. If you want to restrict who can send to the mailbox, you can configure delivery restrictions in the Exchange admin center under the mailbox’s mail flow settings. This is rarely needed for customer-facing mailboxes like info@ or support@, but it can be useful for internal-only shared mailboxes like hr@ or payroll@ where you do not want external email arriving.

Calendar

Shared mailboxes include a shared calendar that all members can view and edit. This is useful for scheduling team events, tracking shared deadlines, or managing a resource like a conference room. The shared calendar appears in Outlook alongside the shared mailbox folders. If your team needs a shared calendar but does not need a shared inbox, a shared mailbox is still the easiest way to create one, though a Microsoft 365 Group calendar is another option.

Accessing the Shared Mailbox

Outlook Desktop (Windows and Mac)

The shared mailbox appears automatically in the left panel of Outlook for users who have been granted access. It may take up to an hour after being added as a member. If it does not appear, the user can add it manually: File > Account Settings > Account Settings > Change > More Settings > Advanced > Add the shared mailbox address.

Outlook on the Web

Log into outlook.office.com with your normal credentials. Right-click on your mailbox name in the left panel, select “Add shared folder,” and enter the shared mailbox email address. It will appear as a separate mailbox in the folder list.

Outlook Mobile (iOS and Android)

In the Outlook mobile app, tap your profile picture, tap the gear icon, tap “Add Mail Account,” and enter the shared mailbox address. It will be added as a separate account without requiring a separate password, since access is granted through your primary account permissions.

Common Shared Mailbox Mistakes

Creating a regular mailbox and sharing the password. This is the single most common mistake small businesses make. It creates a security risk (shared passwords cannot be audited), prevents MFA from working properly, and costs a license unnecessarily. If you currently have a team mailbox that everyone logs into with the same password, convert it to a shared mailbox.

Not setting up Sent Items copying. Without the PowerShell commands above, sent messages from the shared mailbox end up in individual members’ Sent Items folders. This makes it impossible for the team to see what has been sent and leads to duplicate replies or missed follow-ups.

Adding too many members. Every member has full access to every message. If you add 20 people to a shared mailbox, all 20 can read, reply, and delete any message. Only add people who actively need to work with the mail in that inbox. If someone only needs to send from the address occasionally, grant them Send As without Full Access.

Not monitoring mailbox size. A shared mailbox that quietly fills up to 50 GB will start rejecting incoming mail. Set a calendar reminder to check the size quarterly, especially for high-volume mailboxes. In the Exchange admin center, you can see mailbox sizes under Recipients > Mailboxes.

Confusing shared mailboxes with Microsoft 365 Groups. When you create a Microsoft 365 Group (which happens automatically when you create a Team in Microsoft Teams), it also creates a shared email address. But a Group mailbox behaves differently from a shared mailbox. Group mailboxes have a different permission model, a connected SharePoint site, and a Planner. If you just need a team inbox, a shared mailbox is simpler. If you need a full collaboration space with files, chat, and email, a Microsoft 365 Group or Team is the better fit.

When to Use Something Else

A shared mailbox is the right choice for handling incoming email collaboratively. It is not the right choice for every scenario:

• If you need to send announcements to a group of people and do not need a shared inbox, use a distribution list
• If you need a full collaboration space with files, chat, calendar, and email, create a Microsoft 365 Group or a Team
• If you need automated email routing based on content or sender, look at Exchange mail flow rules or a helpdesk ticketing system
• If you need per-message assignment so you can track who is handling what, you have outgrown shared mailboxes and need a ticketing system like Freshdesk, Zendesk, or Microsoft’s own Dynamics 365

Sequentur configures and manages Microsoft 365 shared mailboxes, distribution lists, and Groups as part of our managed M365 services. If your email setup has grown organically and needs to be cleaned up, or if you are not sure which type of mailbox to use for a specific need, reach out through our contact page and we can help sort it out.