There can be several reasons why Outlook isn’t syncing with Office 365, such as network issues, outdated software, or incorrect account settings. You can try restarting Outlook, checking your internet connection, or ensuring your login credentials are correct. If the issue persists, reinstalling Outlook or repairing your Office installation may help.

If you’ve accidentally deleted emails, you can recover them from the "Deleted Items" folder within 30 days. If they’re not there, check the "Recoverable Items" folder. If emails are still missing, you may need to contact your Office 365 administrator for further assistance or data recovery options.

Slow performance in Office 365 can be due to a variety of reasons, such as insufficient system resources, large email inboxes, or network issues. Try closing unnecessary programs, clearing cache, and ensuring you have enough storage space. If performance continues to lag, it may be helpful to check for updates or reinstall the software.

Installation errors can occur due to system conflicts, incomplete downloads, or corrupted files. Start by running the Microsoft Support and Recovery Assistant tool to troubleshoot and resolve installation issues. Also, ensure that your system meets the minimum requirements for Office 365 and that no other Office versions are interfering with the installation.