A shared mailbox makes it easy for a group of people to monitor and send email from a public email address, like info@contoso.com. When a person in the group replies to a message sent to the shared mailbox, the reply appears to come from the shared address, not from the individual person.
Tip: Before you can use a shared mailbox, the Microsoft 365 admin for your organization has to create it and add you as a member. For more information, ask your admin to see Create a shared mailbox, which describes what the admin needs to do.
If you want to monitor the email from your primary mailbox and the shared mailbox at the same time, use this method. After you complete this task, the shared mailbox and its folders are displayed in the left navigation pane each time you open Outlook on the web.
The shared mailbox displays in your Folder list in Outlook on the web. You can expand or collapse the shared mailbox folders as you can with your primary mailbox. You also can remove the shared mailbox from your Folder list. To remove it, right-click the shared mailbox, and then click Remove shared folder.
To receive notifications of new messages in the Inbox of a shared mailbox, you must open the shared mailbox in a separate browser window.
Use this method if you want to view and manage the email for the shared mailbox in its own browser window. This method also lets you receive notifications of new items in the Inbox of the shared mailbox.
Tip: If you mistype the email address of the mailbox, the result is “No match was found”. Try typing the email address again.
Choose New mail above the folder list. A new message form opens in the reading pane.
At the top of the message, choose 
> Show From.
This option shows you that the people who receive the email message will see it comes from the shared mailbox and not from your own email account.
The first time you use the shared mailbox, you need to add the address to the options available in the From drop-down list:
Right-click the From address and choose Remove.
Type the shared address. The next time you reply from the shared mailbox, its address will appear as an option in the From drop-down list.
To add recipients, type the name of anyone who is in your contacts folder or organization’s address list, or type the email address in the To or Cc box. The first time you enter a person’s name, Outlook on the web searches for that person’s address. In the future, the name is cached so it resolves quickly.
Type a subject.
Type the message you want to send.
When your message is ready to go, click Send.
The first time you reply to a message sent to the shared mailbox, you need to add the shared address to the From drop-down box. Here’s how to do that:
Open Outlook on the web and go to your shared mailbox.
Open a message that was sent to the shared address.
Click Reply.
At the top of the message, choose > Show From.
Right-click the From address and choose Remove.
Type the shared address and send the message. The next time you reply from the shared mailbox, its address will appear as an option in the From drop-down list
One of the great things about using a shared mailbox is that anyone who has access to the shared mailbox also has full access to the calendar. You can create, edit, and delete events in the calendar. Use the shared calendar just as you would use your own calendar. Here’s a short list of things you can do with the shared mailbox calendar:
Let your team know when you’re going on vacation or when you’ll be out of the office.
Create a team meeting.
Edit a calendar event that someone else created.
Cancel a meeting that someone else created.
To access the shared calendar, do the following:
Sign in to your mailbox using Outlook on the web, and then select Calendar.
Right-click Other Calendars, and then click Open calendar.
In From directory, search for the shared calendar you want to open. Select the shared mailbox you want to open, and then click Open.
The shared calendar displays in your Calendar folder list.
To access a shared mailbox on a mobile device, open your browser, sign in to Microsoft 365, and then go to Outlook on the web. From Outlook on the web, you can access the shared mailbox.
Only your Microsoft 365 admin has permissions to set up the ability to send automatic replies from a shared mailbox.