Microsoft 365
Microsoft 365 Setup: Mailboxes, Shared Mailboxes, and Aliases
In Microsoft 365, a user mailbox belongs to one person who signs in to it. A shared mailbox is a team inbox, like support@ or office@, that several people open from their own accounts. An alias is an extra address, like info@, that delivers into a mailbox that already exists. Most small businesses need a user mailbox for each person, a shared mailbox for any address more than one person answers, and aliases for addresses one person handles.
On this page
What is the difference between a mailbox, a shared mailbox, and an alias?
| Option | What it is | Who signs in | License | Best for |
|---|---|---|---|---|
| User mailbox | A personal inbox and calendar; file storage depends on the plan | That person | Yes, one per user | Each employee or owner |
| Shared mailbox | A team inbox several people can open and send from | Nobody directly. Members open it from their own account | Usually not, within Microsoft's size limit | support@, office@, billing@ |
| Alias | An extra address on an existing mailbox | The mailbox owner | No extra cost | info@, hello@, sales@ when one person answers |
| Distribution list or group | One address that sends a copy to several people | Nobody. It forwards copies | No | team@ when everyone needs a copy but nobody needs one shared inbox |
Microsoft's licensing rules and limits change from time to time. Check the current terms for shared mailbox size and archive limits before you plan around them.
Which one should you use?
Start from who answers the address.
- One person answers it: add it as an alias on that person's mailbox. No extra license.
- Two or more people answer it and need to see who replied: use a shared mailbox. Everyone can see the same inbox. Configure shared Sent Items so the team can also see replies.
- Everyone needs their own copy, but replies are personal: use a distribution list.
- A person who logs in, has a calendar, and stores files: that needs a user mailbox with a license.
Example: a three-person service business
| Address | Setup | Why |
|---|---|---|
| owner@ | User mailbox | The owner signs in, keeps a calendar, and owns files |
| tech@ | User mailbox | A second person with their own login |
| office@ | User mailbox | The office manager |
| info@ | Alias on office@ | One person reads general inquiries |
| estimates@ | Shared mailbox | Owner and office manager both answer quote requests |
| billing@ | Shared mailbox | The office manager and the bookkeeper both need it |
That is three licenses, not six.
Example from our own work
On one of our own projects, all email runs through Microsoft 365 with one primary mailbox and three aliases: one used as the reply-to address on a newsletter, one listed on the website for anyone who wants a human, and one for general contact. One person reads everything, so aliases were enough. If a second person had started answering those messages, we would have moved the shared addresses into a shared mailbox.
What can go wrong?
Replies come from the wrong address
By default, a reply to a message sent to an alias may go out from the mailbox's main address. Microsoft 365 has a setting that lets people send from aliases, but an administrator has to turn it on. Shared mailboxes need a separate "Send As" or "Send on Behalf" permission for each person who replies from them.
Someone signs in to a shared mailbox with a password
A shared mailbox is meant to be opened from each person's own account. Giving out a shared login makes it impossible to tell who sent what and is harder to secure.
A departing employee's email disappears
When someone leaves, removing their license without a plan can lose their mail. A common approach is to convert the mailbox to a shared mailbox first so the rest of the team can still reach it, then remove the license. Plan this before the last day.
Email lands in spam
New domains without SPF, DKIM, and DMARC records are more likely to be filtered. See Domain Names, Website Hosting, and Business Email Explained for what each record does.
Microsoft 365 setup checklist for a small business
This is the order we follow:
- Confirm who controls the domain and that the domain is in your business name.
- Add and verify the domain in the Microsoft 365 admin center.
- Create user accounts for each person and assign licenses.
- Create shared mailboxes and add members with access and send permissions.
- Add aliases to the right user mailboxes.
- Plan and prepare any email migration before changing where incoming mail is delivered. Migration is quoted separately.
- Set up authentication and multi-factor sign-in, including SPF, DKIM, and DMARC as appropriate.
- Switch mail delivery at the planned cutover, using the MX and other DNS records Microsoft provides.
- Test sending, receiving, and Outlook access on computers and phones, including messages from outside your company.
- Write it down: a one-page list of every address, what it is, and who answers it.
What does Frankly Digital set up?
We connect your domain and configure Microsoft 365 user mailboxes, shared mailboxes, and email aliases. Basic setup in a straightforward environment starts at $250. More extensive configuration is defined in your proposal. Email migration and ongoing administration are quoted separately, and Microsoft 365 licenses and domain registration are paid to those providers. See current Domains & Business Email pricing.
For current limits and configuration, see Microsoft’s shared-mailbox guidance and shared Sent Items settings.
Common questions
Does a shared mailbox need a license?
Usually not, as long as it stays within Microsoft's size limit for unlicensed shared mailboxes. It needs one if it grows past that limit or needs features like archiving. Check Microsoft's current terms.
Can I send email from an alias?
Yes, once an administrator turns on sending from aliases for your organization. Otherwise replies may go out from the main address.
How many aliases can one mailbox have?
More than a small business normally needs. The practical limit is how many addresses one person can manage before a shared mailbox makes more sense.
Can I use Microsoft 365 for email and host my website somewhere else?
Yes. Email and website hosting are separate services connected through DNS.