Shared mailboxes are a popular feature in Microsoft 365, but they are often misunderstood and misconfigured. When set up correctly, they are a great way for teams to manage common email addresses like info@, billing@, or support@. When set up incorrectly, they can create security risks, access issues, and confusion for users.
Here is what shared mailboxes are, when to use them, and the most common mistakes we see.
What Is a Shared Mailbox?
A shared mailbox is an email inbox that multiple users can access. Unlike a regular user mailbox, a shared mailbox does not require its own license as long as it stays under 50 GB and does not use advanced features like online archiving.
Shared mailboxes are typically used for:
- General business addresses like info@company.com
- Department inboxes like accounting@ or hr@
- Former employee mailboxes that need to be retained
- Customer facing mailboxes monitored by multiple staff members
Users access shared mailboxes from their own Outlook or Outlook on the web after being granted permission.
Shared Mailbox vs Distribution Group
This is a common point of confusion.
A distribution group simply forwards incoming email to multiple users. Emails live only in the recipients’ inboxes and there is no shared history.
A shared mailbox has a single inbox that everyone can see. All messages stay in one place, making it easier to track conversations, avoid duplicate replies, and maintain continuity.
If multiple people need to read, respond, and reference the same emails, a shared mailbox is usually the better choice.
Common Mistakes We See
Leaving old employees as owners or members
When staff leave the company, their access to shared mailboxes is often overlooked. This creates a security issue and can violate internal policies. Permissions should always be reviewed during offboarding.
Using shared mailboxes for sign ins
Shared mailboxes are not meant to be signed into directly. Doing so bypasses individual accountability and often leads to password sharing. Each user should access the mailbox with their own account so activity can be audited.
Assuming it appears automatically in Outlook
In some cases, the shared mailbox will auto map in Outlook. In others, it will not. Users may need it added manually, especially when using New Outlook or mobile devices. This is normal behavior, not a misconfiguration.
Not monitoring sent mail
By default, sent emails from a shared mailbox may go to the individual user’s Sent Items folder instead of the shared mailbox. If this is not configured properly, it becomes difficult to track responses and follow ups.
Forgetting about size limits
Unlicensed shared mailboxes have a 50 GB limit. Over time, busy mailboxes can hit this ceiling and stop receiving mail. Mailbox size should be monitored or retention policies should be applied.
Security Best Practices for Shared Mailboxes
To keep shared mailboxes secure and manageable:
- Limit access to only users who need it
- Remove access promptly when roles change or staff leave
- Avoid granting full access broadly “just in case”
- Do not use shared mailboxes as login accounts
- Review permissions periodically
Shared mailboxes should simplify collaboration, not create risk.
When to Review Your Shared Mailboxes
It is a good idea to review shared mailbox setup if:
- Emails are missing or replies are being duplicated
- Former employees still appear to have access
- Users report they cannot see the mailbox in Outlook
- The mailbox has existed for several years without review
- You are migrating to New Outlook or changing licensing
Final Thoughts
Shared mailboxes are a powerful Microsoft 365 feature, but only when they are set up and maintained properly. Many businesses use them every day without realizing there are better, safer ways to manage access and visibility.
If you are unsure whether your shared mailboxes are configured correctly or want help auditing permissions, reach out to your IT provider before small issues turn into bigger problems.
