Office 365 Shared Mailbox: Setup, Permissions, Costs, and Troubleshooting
Set up a shared service or sales mailbox: licensing, permissions, Outlook access, shared sent replies, acceptance testing, and troubleshooting.
When no one is clearly responsible for an inquiry, messages go unanswered and customers receive conflicting replies. When setting up an Office 365 shared mailbox, configure access and sending permissions, save copies of replies, and assign responsibilities within the team. Before using it, verify that two employees can receive an inquiry, reply from the shared address, and see the correspondence.
When is an Office 365 shared mailbox the right choice?
A shared mailbox works well when a team needs to work in the same mailbox and reply using a single business address. Alongside email, the mailbox includes a shared calendar for coordinating visits or team activities. Employees access it through their authorized personal accounts, while sign-in to the mailbox account itself remains blocked. When employees change, update membership and permissions, and check that their replacements can access the mailbox.
Choose a solution based on the workflow you need: shared email handling, collaboration with external parties, or inquiry tracking. For collaboration with people outside the organization, consider a Microsoft 365 group with appropriate guest settings. If each inquiry needs an assigned owner, status, and reporting, check these capabilities in a ticketing system before choosing.
Primary need | Option to consider | What to check before choosing |
|---|---|---|
Shared email and calendar management | Shared mailbox | Access and sending permissions, and saved copies of replies for the team |
Collaboration with people outside the organization | Microsoft 365 group | Whether the solution and guest settings meet the business need |
Ownership and tracking for each inquiry | Ticketing system | Whether the plan includes assignment, status, and reporting |
What should you prepare, and what are the licensing costs?
You need Exchange Online, appropriately licensed personal mailboxes, and an administrator with the Exchange Administrator role to set things up. According to Microsoft’s licensing documentation, a shared mailbox can hold up to 50GB without a separate mailbox license; employees still need licensed Exchange Online mailboxes. Do not assume an Office apps subscription includes email. Prepare a list of employees, your preferred address, business owners, and retention requirements before purchasing or changing licenses.
Increasing mailbox capacity to 100GB requires Exchange Online Plan 2. Expanding an archive or enabling Litigation Hold, a mechanism that preserves information for legal proceedings, requires a licensing check: Microsoft specifies Plan 2 or Plan 1 with the Exchange Online Archiving add-on for the applicable scenarios. Total cost depends on employee licenses and additional capabilities, so request an itemized breakdown based on your needs. Use the Microsoft 365 licensing page to prepare your requirements, distinguishing mailbox capacity, archiving, and retention policies.
How do administrators create the mailbox and configure permissions?
Create the mailbox in the admin center, add employees, and check access and sending permissions separately. Full Access lets users open the mailbox and manage its contents but does not grant permission to send. Send As displays the shared address to recipients; Send on Behalf also identifies the employee sending on the mailbox's behalf. For a service team, deliberately choose how the sender will appear based on how you want to manage customer relationships.
According to the official setup guide, delegation can also be managed in the Exchange admin center. Menu labels may vary between interfaces; the English names help identify the correct option. The following steps are for cloud-based Exchange Online. In a hybrid Exchange environment, Microsoft instructs administrators to create and manage shared mailboxes through the on-premises Exchange admin center. Record who approved mailbox membership, and perform administrative actions using an individual administrator account.
How do employees add the mailbox to Outlook and reply from it?
Employees open the mailbox through their authorized personal account without receiving a shared password. Follow the instructions for the interface you use.
New Outlook for Windows
Check that the From field displays the intended address. In new Outlook for Windows, if the field is hidden, select Options → Show From. If the shared address is not listed, select Other email address and enter it. In other interfaces, follow the relevant instructions in the official Outlook guide. Check with the recipient how the sender’s identity appears for the sending permission used.
Check the sender before sending
Before adding the mailbox on mobile, review Microsoft’s mobile instructions and check that they apply to your email environment. Use the personal account that has been granted access to the mailbox.
Outlook for iOS or Android
Open the mailbox using your authorized personal account, following the Outlook on the web tab in the Microsoft guide. Adapt the instructions to the interface you see.
Outlook on the web
To add the mailbox, follow the Classic Outlook tab in the official Outlook guide, according to your installed version. If access fails, ask your administrator to check permissions and how the mailbox was added.
Classic Outlook for Windows
After permissions have been added, close and reopen the app. If the mailbox does not appear, select Mail, right-click the account name in the folder pane, and select Add shared folder or mailbox. Enter the mailbox address and look for it under Shared with me.
How do you keep correspondence visible to the team and troubleshoot problems?
Working together requires visibility of sent replies and clarity about who is handling each message. According to Microsoft’s mailbox settings guide, sent messages are saved in the sender’s mailbox by default, so enable copies in the shared mailbox. Agree on a procedure: identify the person handling an inquiry before replying, move completed inquiries to a completed-work folder, and review open inquiries at shift changes. Marking a message as read neither assigns ownership nor prevents duplicate replies.
For an acceptance test, send an inquiry from an external address to the shared mailbox and verify that two employees can see it. One employee should reply from the shared address; the other should check that the reply appears in Sent Items, while the recipient checks the sender address. Reply from outside and check that the follow-up arrives. Record the test date, interfaces, testers, and outcome.
Symptom | What to check | Corrective action |
|---|---|---|
Mailbox does not appear | Authorized account, Full Access, and how permissions were assigned | Check access and add the mailbox following the instructions for your interface; automapping does not work when permissions are assigned through a group |
Can read but cannot send | Send As or Send on Behalf | Check and add the required sending permission; permission changes may not take effect immediately, so recheck permissions and access |
Personal sender address appears | The From field in the message itself | Select the shared address and verify it with the recipient |
Replies are not visible to the team | Sent items settings and the sending permission used | Enable saved copies and run another sending test |
If the issue persists, recheck permissions and actual access. Waiting alone will not fix a missing permission. For permission management, see Microsoft’s documentation on mailbox permissions.
When an employee leaves, block their sign-in and follow your organization’s offboarding procedure. If their mailbox needs to be converted to a shared mailbox, review the process in Microsoft’s conversion guide before proceeding. Before changing licensing, check mailbox size and archiving and preservation requirements: a shared mailbox can hold up to 50GB without a separate license, while increasing it to 100GB requires Exchange Online Plan 2. Additional capabilities may require appropriate licensing.
Check the privacy requirements that apply to the information in the mailbox, and align access permissions with employees’ roles and the business need. Update permissions when employees change roles or leave, and check access for their replacements. For more information, see the Privacy Protection Authority’s guide.
Frequently asked questions
Do Office 365 and Microsoft 365 refer to the same service here?
Is the mailbox free?
Do you need a shared password, and can you add an external Gmail user?
When should you move to a ticketing system?
Updated: 28.10.2026.