The Microsoft 365 admin center was formerly known as the Office 365 admin center.
SelectGroups>Shared mailboxesin the navigation pane.
SelectAdd a mailboxon theShared mailboxespage.

On theAdd a mailboxpage, bang out a name for the shared mailbox in theNamefield.
A mailbox alias is automatically created in theEmailfield, but you could change the alias if you like.
When you’ve named the shared mailbox, selectAdd.

SelectAdd members to this mailboxunderNext steps.
SelectAdd memberson theAdd Shared Mailbox memberspage.
UnderMembers, check the box beside each person who will have access to the shared mailbox.

When you’re done, selectSaveand thenClose.
If you want to save these emails to the shared mailbox, you must edit the shared mailbox options.
Select your shared mailbox.

Set bothCopy items sent as this mailboxandCopy items sent on behalf of this mailboxtoOn, then selectSave.
The shared mailbox appears automatically in the Outlook sidebar.
SelectNew Emailto create a new message.
SelectFromin the new email message, and then go for the shared mailbox.
punch in your message and selectSend.
Right-clickFolders(or your mailbox name) in the navigation pane, and then selectAdd shared folder.
jot down the email address of the shared mailbox in theAdd shared folderdialog box, and then selectAdd.
TapAdd Accountin the left pane, then tapAdd a Shared Mailbox.
If you have multiple Outlook accounts, choose the one that has access to the shared mailbox.
Enter the email address.
Once the process is complete, you should see your shared mailbox under your accounts in the Outlook app.
What Is a Shared Mailbox in Office 365?
Every person assigned to an Office 365 shared mailbox has complete access to all the messages in it.
That said, shared mailboxes typically don’t have user names or passwords, creating some security concerns.
Why Use a Shared Mailbox?
FAQ
There are a few ways toclean up (or clean out) your mailbox in Outlook.
To completely clear a mailbox, right-tap the folder and selectEmpty Folder>Delete All.