Shared mailbox calendar in Outlook: who can use it and its limits
A shared mailbox gives a team one address and one calendar without anyone signing in as that mailbox. It suits a front desk or support rota, but Microsoft sets limits that push larger or mixed teams elsewhere. Arte Soft, the developer of Cloud Calendars, explains.
Is a shared mailbox the right fit?
| Requirement | Shared mailbox (per Microsoft) |
|---|---|
| One team address and calendar | Yes |
| Members inside the organisation only | Yes |
| More than 25 users | No — Microsoft suggests a Microsoft 365 group |
| External members | No — Microsoft suggests a group |
| Prevent members deleting shared-mailbox email messages | No |
| Sign in directly as the mailbox | Not intended; block sign-in |
What most people assume
A shared mailbox is just an account the team shares a password for.
What it is and who can use it
Microsoft describes shared mailboxes for addresses like information, support or reception. An administrator creates one and adds members. Members need their own licensed Exchange Online mailbox. For basic use the shared mailbox can hold up to 50 GB without a separate licence, but archiving, litigation hold and some advanced security or compliance features can require additional licensing.
Microsoft says a shared mailbox isn’t for direct sign-in; its account should have sign-in blocked. Only people inside your organisation can use it; Microsoft suggests a Microsoft 365 group if outside people need access.
Limits to check first
Microsoft says a shared mailbox supports a maximum of 25 users; too many simultaneous users may see connection failures or duplicated messages. Microsoft recommends a Microsoft 365 group if more users are needed. Its deletion warning is about email messages: you cannot prevent members from deleting those messages. It separately documents that members can create, view and manage shared-calendar appointments. Microsoft also documents limitations on encryption of mail sent from a shared mailbox.
Using the calendar, by client
New Outlook and classic Outlook: after the administrator adds you, restart Outlook; Microsoft says the shared calendar is added to your Calendars list automatically. Choose it in calendar view. Any member can create, view and manage appointments.
Outlook on the web: add the shared mailbox with Add shared folder or mailbox, then use its calendar. Microsoft notes that to get new-message notifications you open the mailbox in a separate browser window. Microsoft also documents Outlook for iOS and Android access.
Worked example: an office front desk
A fictional office of 12 receptionists wants one visitor calendar. An administrator creates “Reception”, adds the 12 as members and leaves sign-in blocked. Each receptionist restarts Outlook and finds the Reception calendar listed.
A contractor at another company asks for access. Shared mailboxes can’t include external people, so the office instead sends the contractor specific invitations.
Check: one receptionist adds a test visitor slot and another confirms they can see and edit it; then the test is deleted.
What it looks like
Cloud Calendars overview, using our product images. Provider settings and protocol examples described in this guide are separate from the screens shown here.
What to do
- Ask an administrator to create the mailbox and add members.
- Keep sign-in to the shared account blocked.
- Stay within 25 users and internal members.
- Restart Outlook to see the calendar; in the web, add the shared mailbox.
- Test an entry from two members’ accounts.
Questions
- Can someone outside our company use the shared calendar?
- No. Microsoft says only people inside your organisation can use a shared mailbox.
- How many people can share one?
- Microsoft says a maximum of 25 users.