If you're using an Exchange account that requires advanced settings, you'll need to remove the account and add it again using advanced settings. To add the account using advanced settings, see Add an account using advanced setup. If you have a Google, Yahoo! Mail, iCloud, IMAP, or POP3 account, check the settings in the advanced mailbox settings to make sure they're configured to your email provider's specification. If you're using an Outlook.com, Microsoft 365, or Exchange account, you won't have advanced mailbox settings unless the account was set up using advanced setup. If your problem is how quickly mail populates, change the download preference to headers then full items.

Check your privacy settings

From there, make sure that the proper calendars are selected. If none of these steps address the syncing problem, escalate the issue to the IT team. Third-party firewalls or antivirus software might prevent you from syncing your email and calendar events.

Allow Mail and Calendar apps through Windows Firewall

If it is lower than 50 GB, you may have too many sync issues in which case you must delete the cache and re-run the sync, you can clear sync issues and test before deleting the cache. Some of the most common issues users encounter with Outlook Office 365 not syncing fix on iOS relate to syncing. Learn how to troubleshoot when the iPhone Outlook app is not syncing. The approach that IT takes to address a syncing problem depends on what type of problem it is. If it's a client-side issue, the admin can usually instruct the user on what steps to take.

Additional resources

• While we all use systems differently, I don’t think I have 100GB of data after working for my company almost 25 years, let alone this much email.
• If that doesn't solve your issue, try the solutions below.
• An app password is used instead of your normal account password for apps that don't support two-factor authentication.
• The approach that IT takes to address a syncing problem depends on what type of problem it is.
• The Mail and Calendar apps for Windows 10 don't support two-factor authentication.
• When issues occur at the account level, admins should ensure that users are properly logging into their accounts and provide them with instructions as needed.
• Firewalls and antivirus software might prevent you from syncing your email and calendar events.
• Regardless of their mailbox size, Microsoft set a default OST size for a reason, while it can be changed, that doesn’t mean it should.
• Why not limit the caching to a more reasonable 1 year, if they need to access things outside of this, they can, they just have to click ‘view messages on server’ to do so.

When using Microsoft Teams on an iPhone, slow performance and app crashes can bring mobile work to a halt. Many issues come down to internet bandwidth or low storage space. If there's a feature you think is missing from the Mail and Calendar apps, or if a feature in isn't working properly, you can provide feedback directly to the Mail and Calendar team.

Check if two-factor authentication is turned on for your account

Windows Defender Security Center is free security software that's included with Windows 10. If you haven't installed alternative security software, you should temporarily turn off Windows Defender Security Center. We're sorry you're having problems with the Mail and Calendar apps for Windows 10. To fix the issue, please try each of the following solutions in order. Why not limit the caching to a more reasonable 1 year, if they need to access things outside of this, they can, they just have to click ‘view messages on server’ to do so. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.





Change the limit to 1 year, wait for the sync, check the size of the OST once Outlook confirms all sync has been completed. Now change the slider to 2 years and follow the same principal. Outlook has a hard limit of 50GB per OST, decrease the period of e-mails that get cached, delete the cache, and re-run the sync.