How do i create a shared mailbox in Office 365 Exchange Online?


Sometimes the responsibility to review and respond to email is shared among several people. Sometimes email is related to a process, rather than a specific person. In such cases it is a best-practice to create a Shared Mailbox, rather than using an individual's mailbox to receive/send such email. Shared Mailboxes do not incur a licensing cost on Office 365 as long as you stay within the 5GB mail limit. Shared mailboxes must be created either via PowerShell or via the new GUI tool.

Naming conventions

It's best to agree on a naming convention for your shared mailboxes up-front. Here's what i use across my Exchange Online configurations:

Alias res-[resource type]-[geolocation]-[short name] res-sharedmbox-phl-ar No spaces or special characters allowed. This will become part of your shared mailbox's email address.
Name Shared Mailbox: - [geolocation] - [longer name] Shared Mailbox - PHL: Accounts Receivable This will be displayed in the address book and Outlook. It can be longer than the alias, but don't make it too long as the right side of the name will be cut off in Outlook (just because of practical display sizes and widths).

It's readable, scriptable, findable, et cetera. Some people like to add a special character as the first character in the display name (for grouping purposes, for example). I tend to avoid doing so as that may cause unknown issues down the road if your special character isn't supported by Microsoft or a 3rd party tool. Besides, if you always start your conference room names with Shared Mailbox - they'll all be grouped together anyway. If you only have one office and never ever plan on having another one, you can skip geolocation. If you're not sure, use one anyway - 3 or 4 characters is enough to differentiate between most locations. By locations here i don't mean office buildings, i mean states or cities or other locales. You can embed building name or number in the [short name] placeholder, or add one more placeholder if you like

Steps to create a shared mailbox using PowerShell

  1. Start PowerShell and connect to your Exchange Online tenant (or download and install the PowerShell profile for Office 365 / MS Online Services)
  2. Create a new mailbox (note the really important -Shared switch!)
    1. new-mailbox -alias res-sharedmbox-phl-ar -name "Shared Mailbox - PHL: Accounts Receivable" -Shared
  3. Set mailbox limits
    1. Set-Mailbox res-sharedmbox-phl-ar -ProhibitSendReceiveQuota 5GB -ProhibitSendQuota 4.75GB -IssueWarningQuota 4.5GB
  4. Assign mailbox permissions
    1. add-mailboxpermission res-sharedmbox-phl-ar -user [user or group alias] -accessrights FullAccess -automapping $false
  5. Assign "Send As" permissions (optional)
    1. Add-RecipientPermission res-sharedmbox-phl-ar -Trustee [user or group alias] -AccessRights SendAs

Note about the -automapping switch used in 4.1: if you set it to $true or omit it, the user specified by the -user switch will have the mailbox show up in Outlook next time system attendant runs (which is usually the next day). Sometimes that's a desireable feature, and sometimes it's not. Including it in the command line explicitly gives you the peace of mind that you're making a conscious choice.

Note that it may take an hour or so for permissions to propagate to group members

Steps to create a shared mailbox using the GUI-based tool

I'm going to let the most excellent article on the Community Office365 support site provide details on this step. I've used the tool, and it works, and i still prefer PowerShell. If you think the tool needs additional instructions, let me know and i'll update this article.


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