When sending an email or while syncing the following "Error in fanout" is returned

In the Mailsync Logs on the Nylas Dashboard or in the API Logs when sending an email you may see/receive the following error message:

This error message can occur when there is a configuration issue on the exchange end and prevent sending and syncing. To resolve the issue, try the following suggestions:

1. Ensure the mailbox is on Office 365, not on-premise. If you are in a hybrid environment, make
   sure that the mailbox is on the Office 365 side.
2. Move the mailbox to another mailstore where possible. This can help resolve issues related to corrupted data or other issues with the mailbox.
3. Check if it's a shared mailbox. Shared mailboxes can sometimes cause issues if the user does not have the correct permissions or if there are issues with syncing the mailbox.
4. For new users, ensure that the mailbox has been provisioned and has something in it. This can help avoid issues related to a missing mailbox or other provisioning issues.
5. Check for transient infrastructure issues at Microsoft related to storage. Sometimes, this error can occur due to issues with the Microsoft infrastructure.

If none of these suggestions resolve the issue, a known solution is to provision a new
mailbox. This can help ensure that the mailbox is set up correctly and avoid any issues related to corrupted data or other issues with the mailbox.

Updated April 19, 2023 15:45