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Microsoft 365 Application

Outlook

Use this guide when Outlook will not open your mailbox, keeps asking you to sign in, stops syncing, or shared mailboxes and calendars are missing.

Reviewed April 2026

Application Guide

Overview

Outlook is Microsoft's desktop email and calendar app for your work mailbox, meetings, contacts, and shared mailboxes.

Most Outlook problems come down to the wrong account being signed in, the local Outlook profile falling out of sync, or an add-in blocking normal startup.

Plain English

What this app is usually used for

Exchange-backed desktop mail and calendar workflow where profile state, Modern Auth, and add-ins drive most support work.

It is part of the Microsoft 365 family covered in our app help.

Common problems

Common problems

Sign-in prompts keep coming back

Outlook repeatedly asks for a password or opens the wrong account even though your password is correct.

Likely fix

Confirm Outlook on the web works first, then sign out of any wrong Office account and sign back in with the correct work account.

What to collect

Send a screenshot of the prompt, the work email account you expected to use, and whether Outlook on the web works.

Outlook hangs on Loading Profile or crashes

Outlook opens slowly, never finishes loading, or closes shortly after launch.

Likely fix

Restart the computer, try opening Outlook without add-ins, and install pending Office updates before recreating anything.

What to collect

Send the exact Outlook version, when the issue started, and a screenshot if there is a crash message.

A shared mailbox or calendar is missing

Your primary mailbox opens, but a shared mailbox, shared calendar, or delegated send option is gone or out of date.

Likely fix

Check whether the same shared mailbox appears in Outlook on the web, then restart Outlook and let it refresh before changing profiles. In new Outlook, right-click your account and use Add shared folder or mailbox if it still does not appear after your support team confirms you are a member.

What to collect

Send the shared mailbox or calendar name, what should be visible, and whether the same problem shows in Outlook on the web.

Switching between new Outlook and classic Outlook

A feature or rule is missing after the desktop switched between new Outlook and classic Outlook, or Outlook opens in the version you did not expect.

Likely fix

Use the New Outlook toggle in the top-right of the window to switch back to classic Outlook, or use Try the new Outlook in classic to move to new Outlook. Allow the app to restart fully, then re-check signatures, rules, and shared mailboxes in the version you are keeping.

What to collect

Send which version is open now, which version you expected, and the exact feature or rule that is missing.

A secondary work account or online archive will not appear

You expect a second work account, a delegated mailbox, or an online archive to appear and it does not, or it shows the wrong account name.

Likely fix

In new Outlook, go to Settings > Accounts and add the account there. In classic Outlook, use File > Add Account. Online archives typically appear automatically when assigned and may take time to populate, so confirm with support that the archive is enabled before reconfiguring Outlook.

What to collect

Send the account or archive name, which Outlook version you are using, and whether the same account works in Outlook on the web.

First things to try

First things to try

Quick checks before you change anything

  • Are you signed in with the correct work email account?
  • Can you open the same mailbox in Outlook on the web?
  • Did the issue begin after a password change, restart, update, or new computer?
  • Is the problem sign-in, mail flow, search, calendar, or a shared mailbox?

Try these fixes first

  • Compare Outlook on the web to the desktop app. If the web version works, the problem is usually local to the app or profile.
  • Remove old or incorrect work or personal accounts from Office if more than one account appears.
  • Try opening Outlook with add-ins disabled if it hangs on Loading Profile or crashes right away.
  • If search is slow or results are missing, leave Outlook open for a few minutes after sign-in so it can finish syncing.
  • If you switched between new Outlook and classic Outlook recently, decide which one is your daily driver and confirm sign-ins, signatures, and rules in that version before troubleshooting further.

Slow down

Do not do this yet / warnings

Avoid these until support says it is safe

  • Avoid deleting local Outlook data file or profiles blindly if the user has large shared mailboxes, PST dependencies, or unstable connectivity.
  • Collect exact error wording, organization, affected apps, web-versus-desktop behavior, and recent password, multi-factor sign-in, or device changes before Tier 2 takes over.
  • Do not reset OneDrive or recreate Outlook profiles until permissions, licensing, and organization selection are confirmed.
  • Preserve signatures, PST or archive references, shared mailbox notes, and profile expectations before computer cleanup.

What support needs

What details support needs

Send these details

  • A screenshot of the exact Outlook message or screen where the problem happens.
  • The work email account you used to sign in and whether Outlook on the web works with that same account.
  • Your Outlook version from File > Office Account or File > About Outlook.
  • If shared mailboxes or calendars are involved, the name of the mailbox or calendar that should appear.

Licensing & access

Licensing / access notes

Licensing / access checks

  • Make sure the mailbox is still active and tied to the work account you are using in Office.
  • If Outlook says it is unlicensed, open another Microsoft 365 app and confirm the same work account is signed in there too.
  • If only a shared mailbox is missing, note the mailbox name and whether it still appears in Outlook on the web.

Phone / Tablet

Phone / tablet setup

  • Install Outlook from the App Store or Google Play and add the same work email account you use on your computer.
  • Finish any company sign-in, approval, or device-registration prompts before assuming setup failed.
  • Allow notifications and calendar access if you expect Outlook on your phone to show mail alerts or calendar events.
  • If you recently changed phones, note whether the old phone still receives mail or prompts before you contact support.

More checks

More setup checks

Install / update basics

  • Close Outlook fully, install any pending Office updates, and restart the computer.
  • Open Word or another Microsoft 365 app first and confirm the correct work account is signed in.
  • When Outlook reopens, test send and receive, calendar, and one shared mailbox if you normally use one.

More things to check

  • Compare Outlook on the web versus desktop. If Outlook on the web is good, stay local; if Outlook on the web is bad too, move into mailbox, license, or service-health checks.
  • Review add-ins, local Outlook data file size, cached mode, and whether the user recently switched from classic to new Outlook.
  • Check Teams add-in, Adobe PDF, CRM, or antivirus mail plug-ins before deeper rebuild work.
  • Collect mailbox work account email, Outlook on the web result, Outlook version, add-ins in scope, and whether the same symptom follows the user to another machine.
  • Avoid deleting local Outlook data file or profiles blindly if the user has large shared mailboxes, PST dependencies, or unstable connectivity.