Welcome to Helpful Thursdays, Anantek Solutions’ practical guide series for small businesses.
A shared mailbox gives your team one professional address, such as info@, hello@, sales@ or support@: that several people can access using their own Microsoft 365 accounts. It keeps customer messages visible to the right people and avoids relying on one employee’s personal inbox.
This guide explains how to complete a Microsoft 365 shared mailbox setup, assign permissions and help your team access it in Outlook.
Important: Microsoft regularly updates its admin centre menus. The names and layout may vary slightly from the screens shown below.
What Is a Microsoft 365 Shared Mailbox?
A shared mailbox is a team inbox that allows multiple users to:
- Read and manage incoming messages
- Reply from a shared business address
- Use a shared calendar
- Organise messages into folders
- Continue working when one team member is unavailable
Unlike a normal user mailbox, a shared mailbox is not designed for direct sign-in. Each team member signs in with their own licensed Microsoft 365 account and receives delegated access.
This makes shared mailboxes useful for:
- General enquiries:
info@yourbusiness.co.uk - Customer support:
support@yourbusiness.co.uk - Sales:
sales@yourbusiness.co.uk - Reception:
reception@yourbusiness.co.uk - Accounts:
accounts@yourbusiness.co.uk
A shared mailbox is different from a distribution list. A distribution list forwards messages to individuals, while a shared mailbox provides one central inbox where your team can see previous conversations and manage responses.
Before You Start: What You Need
You will need:
- A Microsoft 365 business subscription that includes Exchange Online email.
- An account with an Exchange Administrator role, or access to someone who has one.
- The email address and display name you want to use.
- A list of the staff members who need access.
- A decision about whether users should Send As or Send on Behalf.
Microsoft 365 Apps for business alone does not include Exchange Online email, so it may not be sufficient to create a shared mailbox.
Step 1: Create the Shared Mailbox
- Sign in to the Microsoft 365 admin centre.
- Select Show all if the full navigation menu is not visible.
- Go to Teams & groups.
- Select Shared mailboxes.
- Choose Add a shared mailbox.
- Enter a display name, such as Customer Support.
- Enter the email address, such as
support@yourbusiness.co.uk. - Select Save changes.
Microsoft may take a few minutes to create the mailbox before you can add members.
Illustrative screen showing the typical Microsoft 365 shared mailbox creation process. Your organisation’s interface may look different.
Choose the address carefully. It should be easy to remember, clearly connected to a business function and suitable for long-term use. Avoid creating a mailbox named after an individual unless it is intended to be a personal account.
Step 2: Add Team Members
Once the mailbox has been created:
- Open the new shared mailbox from the Shared mailboxes page.
- Find Members or Manage mailbox permissions.
- Select Add members.
- Choose the staff members who need access.
- Confirm the changes.
Start with the smallest practical group. Giving access to every employee makes it harder to control responsibility and increases the risk of accidental changes.
Microsoft states that shared mailboxes support up to 25 users. If a much larger group needs to collaborate, a Microsoft 365 group or another workflow may be more suitable.
Step 3: Choose the Correct Sending Permission
There are three main permissions to understand.
Full Access
Full Access allows a user to open the mailbox, read messages, manage folders and use the shared calendar.
Full Access does not automatically allow a user to send messages from the shared address.
Send As
Send As makes an email appear to come directly from the shared mailbox.
For example, a reply sent by Sarah from support@yourbusiness.co.uk will appear to the recipient as:
Customer Support
<support@yourbusiness.co.uk>
This is usually the best option for customer-facing addresses because it creates a consistent business identity.
Send on Behalf
Send on Behalf shows both the individual and the shared mailbox. For example:
Sarah on behalf of Customer Support
This can be useful when recipients need to know which person handled the enquiry.
For most SMEs, the usual setup is:
- Full Access for staff who manage the inbox
- Send As for staff who need to reply as the business
- Send on Behalf only where individual accountability is important
Full Access and Send As are normally managed through mailbox delegation. Send on Behalf may require the Exchange admin centre or PowerShell, depending on your Microsoft 365 configuration.
Illustrative permissions screen showing the three key shared mailbox access options.
Step 4: Open the Mailbox in Outlook
Outlook desktop
In many organisations, a shared mailbox appears automatically in Outlook after permissions have been applied and Outlook has been restarted.
If it does not appear:
- Close and reopen Outlook.
- Wait for the permission changes to synchronise.
- Ask your administrator to confirm that you were added directly to the mailbox.
- Check whether the mailbox is visible in the folder list.
When composing a message, select the From field and choose the shared address. If the address is not visible, select Other email address and enter it manually.
Outlook on the web
To access the mailbox through a browser:
- Sign in to Outlook on the web with your own Microsoft 365 account.
- Select your profile picture in the top-right corner.
- Choose Open another mailbox.
- Enter the shared mailbox address.
- Select Open.
You can also add it to your folder list using Add shared folder or mailbox.
Illustrative Outlook view showing a shared mailbox and how staff can send from the shared address.
Allow some time for new permissions to take effect. Microsoft notes that sending errors caused by permission replication can sometimes resolve after around an hour.
Step 5: Add the Shared Mailbox to Outlook Mobile
Staff can use a shared mailbox on iOS or Android if:
- Their primary mailbox is in Exchange Online.
- The shared mailbox is also in Exchange Online.
- They have the required permissions.
- They are using the Outlook mobile app.
In Outlook mobile:
- Sign in using your normal work account.
- Open the left navigation menu.
- Tap Add Account.
- Select Add a Shared Mailbox.
- Choose the account that has permission to access the mailbox.
- Enter the shared mailbox address.
- Tap Add Mailbox.
The mailbox should then appear in the account list.
Illustrative Outlook mobile walkthrough. The exact menu layout can vary between iOS and Android.
Licensing and Storage Limits
A shared mailbox does not normally need its own licence when it is 50 GB or smaller and does not require features that need additional licensing.
However, each person accessing it must have their own licensed Exchange Online mailbox. In practical terms:
- The shared mailbox itself can be unlicensed up to 50 GB.
- Every staff member using it needs an appropriate Microsoft 365 or Exchange Online licence.
- An Exchange Online Plan 2 licence is required to increase the mailbox limit to 100 GB.
- Additional licensing may be needed for archiving, litigation hold, retention policies or advanced compliance features.
Monitor mailbox usage before it reaches its limit. Once a mailbox reaches capacity, it may stop sending and eventually stop receiving email.
Security Best Practice for Shared Mailboxes
Follow these basic security rules:
- Never share or distribute a shared mailbox password.
- Keep direct sign-in blocked.
- Require staff to use their own Microsoft 365 accounts.
- Protect individual accounts with multi-factor authentication.
- Grant access only to people who need it.
- Review membership when someone changes role or leaves.
- Use Send As consistently for customer-facing addresses.
- Create clear rules for assigning, responding to and closing enquiries.
- Avoid using a shared mailbox for sensitive information unless your licensing and compliance controls support it.
A shared mailbox is a collaboration tool: not a replacement for proper identity management.
Converting a User Mailbox to a Shared Mailbox
You can convert an existing user mailbox into a shared mailbox. This is useful when an employee leaves but the business needs to retain access to their historical email.
The typical process is:
- Go to Users → Active users in the Microsoft 365 admin centre.
- Select the user account.
- Choose Convert to shared mailbox.
- Confirm the conversion.
- Add the appropriate team members.
- Assign Full Access and Send As permissions.
- Confirm that the mailbox and important messages are accessible.
- Remove the former user’s licence only when you are certain it is no longer needed.
Do not delete the user account before completing the conversion and checking access. If the mailbox exceeds 50 GB or requires advanced compliance features, licensing may still be necessary.
Common Problems and Quick Fixes
The mailbox is not visible in Outlook:
Restart Outlook, check the permissions and allow time for synchronisation.
The user can read messages but cannot send:
Full Access has probably been assigned without Send As or Send on Behalf.
Messages are being sent from the wrong address:
Use the From field and select the shared mailbox before sending.
The mailbox cannot be created:
Check that the account has an Exchange Administrator role and that the address is not already in use.
The mailbox is approaching 50 GB:
Review old messages, apply an agreed retention process or discuss licensing and archiving requirements with your IT provider.
Set Up Microsoft 365 with Confidence
A well-configured shared mailbox gives your team a reliable, professional way to manage common enquiries without creating unnecessary user accounts or duplicated inboxes.
If you need help with a Microsoft 365 shared mailbox, licensing, permissions or wider IT support for small business, contact Anantek Solutions. We can review your Microsoft 365 environment, secure your accounts and provide managed IT services that keep your systems dependable behind the scenes.
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