Know about Office 365 Shared Mailbox Limitations

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The business accounts present in Microsoft 365 plans are not limited to individual users only. The Administrator can create some shared accounts accessible to various users, and users can also send emails through standard accounts. These traditional accounts are called Shared Mailbox, and when the users send emails through such shared mailboxes, the receiver does not know which individual sender has sent the email.

You may have seen examples of shared mailboxes like contact@business.com, complaint@business.com, and info@business.com, etc. These mailboxes are free to a specified size limit and have some restrictions as well. Here is everything you need to know about Office 365 Shared Mailbox limitations.

What is a Shared Mailbox in Office 365?

A shared mailbox is a unique mailbox that is created by the Office 365 administrator to allow multiple users to send & receive messages from the same address. It allows companies to share the load of customer inquiries through emails. They can also be used to store the data that is migrated from on-premises public folders.

Shared mailboxes are not associated with individual users, and it is configured to be accessed by several users like the Sales team, Accounts team, HR, etc.

When you send a message from a shared mailbox, the other person will receive it from Shared mailbox, not from a specific user. Though a shared mailbox is created by the administrator, it has no owner and no password. However, a user must have permissions from the administrator to access a shared mailbox.

Also, shared mailboxes in Office 365 are free and don’t require a license – but, there are some limits to using shared mailboxes. For example, the size limit of a free shared mailbox is 50GB, and it cannot be used as a primary mailbox.

Things to Know Before Creating Shared Mailboxes

If you’re an administrator, then only you’ll be able to create a Shared Mailbox in Office 365 via Exchange Admin Center, Microsoft 365 Admin Center, or PowerShell. Creating a Shared Mailbox is straightforward and simple with proper guidance.

Alongside, it can also be a hectic process if you don’t follow the correct steps and don’t have the required permissions and access. Here are some important facts that every user should know before creating a Shared Mailbox:

• Administrators can add multiple users to a Shared Mailbox in Microsoft 365.
• Shared Mailboxes are free up to 50 GB and do not require a separate license.
• Users cannot login directly without Full Access or Send As permissions.
• If the size limit exceeds, then you need to upgrade to the Exchange Online Plan 2 license.

Permission and Access Restrictions in Shared Mailboxes

Multiple users can read and send emails from a common address without requiring individual credentials. But, users need some permissions to access Shared Mailbox.

Permission Type

• Full Access: Users can open, read, create, and delete items in the mailbox but don’t have permissions to send emails.
• Send As: User can send email that appears to come directly from the shared address as “support@company.com”.
• Send on Behalf: Users can send email where the from address shows as “ABC on behalf of support@company.com”.

Access and Management Restrictions

• No Direct Login: Users cannot directly login Shared Mailbox as they don’t have any username or password. They need their own authorized Outlook account.
• Folder-Level Permissions: Specific folders can have granular permissions set such as Read, Edit, and Note permissions assigned to Inbox.
• Automapping: Outlook automatically maps the Shared Mailbox when Full Access is granted, making it appear in the user’s folder list.
• Security and Access Control: Admins can limit access based on location or device compliance with Azure AD Conditional Access policy.

Size Limits and Storage Restrictions for Shared Mailboxes

Generally, Shared Mailboxes provide 50 GB of free storage without needing additional license. Once you hit it, you need to purchase a new license plan. Here are some Office 365 Shared Mailbox size limits and restrictions:

• Maximum capacity: 100 GB with Enterprise E3/E5 or Plan 2 license.
• Archiving: With Exchange Online Plan 2 license, you can enable Auto-expanding archiving for extra storage.
• Restrictions: These mailboxes are not meant for archiving or large scale data backup, which can violate usage policy. Moreover, if the size limit exceeds, users can send or receive new emails.

Email Sending and Receiving Limits for Shared Mailboxes

Shared Mailboxes share the same sending/receiving limits as individual user mailboxes, i.e., 10,000 recipients/day, 500 recipients per message. When the mailbox size limit exceeds, first sending is blocked, followed by receiving. Plus, the default message size limit is 25 MB or 35 MB depending upon configuration.

Tips for Maintaining Shared Mailbox Performance

Maintaining high performance of Shared Mailbox in Office 365 requires proactive management of mailbox. Here are some best practices that you can follow to keep your mailbox organized:

• Monitor storage: Set up an alert at 45 GB (or as per your requirements) using PowerShell or Microsoft 365 Reports.
• Disable cached mode: Turn off cached mode for users who only access the Shared Mailbox occasionally.
• Archive old emails: Allow auto-expanding archive to keep primary mailbox under 50 GB.
• Audit permissions quarterly: Keep on checking for users who no longer need access to the mailbox and remove them.
• Regular mailbox clean up: Run the Clean Up Folder option to remove unnecessary email items from your mailbox.
• Backup important data: It is always mandatory to create a secure backup of data to avoid corruption issues. Doing it manually can be hectic, we suggest using an advanced Office 365 email backup tool.

Kernel Office 365 Backup and Restore is a great tool that is specially designed to backup Office 365 mailboxes and also restore them back up to Office 365. With this tool, you can easily backup Office 365 Shared Mailbox, Primary Mailbox, or Archive Mailbox, along with Office 365 Groups and Public Folders. Moreover, it offers multiple advanced filters to backup only the needed data.

Concluding: Office 365 Shared Mailbox Limitations

Shared mailboxes in Office 365 provide many advantages to users, but they are free only up to 50 GB. Once you reach the size limit, you will no longer be able to send or receive new emails. Moreover, they have many other restrictions as well like access and permissions required, users can’t login directly, etc. Therefore, organizations need to backup their shared mailbox in Office 365, which can be done using Kernel Office 365 Backup & Restore software. You can skip duplicate items while backing up Office 365 data using this tool. Take the free demo version now to know more.

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