The boss's mailbox on the assistant's screen, the shared info@ inbox for the whole team - shared mail is where offices feel app differences within an hour of switching.
Shared mailboxes and delegation are normal office life: a team watches info@ and support@, an assistant manages the director's calendar, someone sends on behalf of the department. Both Outlooks support shared mailboxes in Microsoft 365, but the depth differs - folder behaviour, sending identity, delegate calendar tools and the small permissions quirks that assistants depend on. This page compares them task by task, so a switch does not strand the people who run everyone else's mail.
Example panel - shared mailbox behaviour also depends on your Microsoft 365 permissions, not only the app.
In Microsoft 365, a shared mailbox you have permission for usually appears automatically in classic Outlook after a restart, and can also be added manually. In the new Outlook, shared folders and mailboxes appear under a Shared with me style section, and the experience has been improving - what began as basic folder access now covers adding the mailbox more completely in many builds. The catch is variation by build and permission type: Full Access, folder level permissions and calendar-only sharing do not behave identically. Test with your real permissions, not with an admin test account that sees everything.
Reading shared mail is easy. Sending correctly is where mistakes happen. Send As makes mail appear from the shared address. Send on Behalf shows the assistant's name for the mailbox owner. Classic Outlook makes the From field and account switching explicit and keeps sent items in the right place with the right settings. In the new app, sending from a shared address works, but sent item placement and default From behaviour have historically needed checking per build, and a wrong default can put a client reply under a personal name. Test one real send of each type and inspect what the recipient actually receives.
Directors rarely manage their own calendars; assistants do, with delegate access to create, move and respond to meetings, sometimes with private item visibility. Classic Outlook's delegation model is mature: granular permissions, private item access for delegates, and meeting handling on behalf of the owner all behave predictably. The new Outlook supports delegate calendars, but edge cases - private appointments, certain recurring series handling, and permission combinations - have been thinner. If one person's whole job is another person's calendar, that person is your pilot user, and their verdict outweighs every feature list.
Not all sharing is a mailbox. Sometimes it is one folder with a vendor, one calendar with a sister office, or an archive mailbox opened alongside your own. Classic lets you open another user's mailbox tree with fine control and keep it permanently in the folder pane. The new app's handling of these arrangements exists but has been more limited and build dependent. Offices with complex folder sharing maps should draw the map first - who sees what - and verify every line of it in the new app before moving anyone who depends on that map daily.
If shared mail is a side task, the new Outlook is probably already fine. If shared mail is the job - support desks, info inboxes, executive assistance - pilot longer and judge on the shared tasks alone. Also remember permissions are granted in Microsoft 365, not in the app: most access problems after switching are actually old permission styles meeting a new client, fixed by cleaning up the permission, not by reinstalling anything. And whatever you choose, say it plainly to the team: which app owns shared mail in your office, so nobody's reply goes missing between two apps.
See both Outlook apps side by side in the full video - every difference shown on a real PC, step by step.
Watch Full VideoYes for Microsoft 365 shared mailboxes, with an experience that has improved in stages. Depth varies by build and permission type, so test your exact arrangement before moving a team.
Yes, with Send As permission the shared address can be used in the From field. Verify the recipient view and where the sent copy is stored in your build.
Usually a permission style or a staged feature difference. Check the exact permission granted in Microsoft 365 and test after an app update; complex folder sharing is an area where classic is still fuller.