Outlook is not syncing properly

When Outlook stops syncing, users may see old inbox content, missing folders, or delayed sending and receiving. The cause may be an unstable profile, poor connectivity, a corrupted cache, or an authentication problem between Outlook and Microsoft 365.

Before making bigger changes, confirm the internet connection, check whether Outlook on the web works, and see if the problem affects one device or every device on the same account.

Repeated login prompts

If Microsoft 365 keeps asking for credentials, there may be a token issue, MFA conflict, account lockout, outdated saved credentials, or a sign-in policy problem. Many people waste time re-entering passwords when the real issue is session authentication or device trust.

Mailbox access and permissions problems

Shared mailboxes, delegated access, and new-user setup often create confusion. If one person can see a mailbox and another cannot, review account permissions, licensing, and whether Outlook has refreshed the profile after recent changes.

  • Check if the user can access the mailbox in Microsoft 365 webmail
  • Confirm shared mailbox permission changes have had time to apply
  • Review whether the correct account is signed into Outlook

Sending errors and delivery delays

When messages stay in the Outbox or bounce, the root cause can include profile corruption, attachment limits, spam filtering, DNS issues, or simple connection instability. Business users should also check whether the problem is affecting one mailbox or multiple users.

When to get expert help

If the problem involves multiple users, shared mailboxes, security policies, MFA, or admin-side configuration, it is usually faster to bring in support instead of experimenting across multiple devices. For direct help, see Microsoft 365 & Email Support and Microsoft 365 Administration.