Connection did not succeed. Try again later.
This error may occur for the following reasons:
- Mailbox Permissions. The admin account used to migrate multiple mailboxes is not a global admin, or it does not have a mailbox you can log in to using OWA, or it has insufficient permissions.
- Connection Throttling. The admin account was used to migrate multiple mailboxes, and Exchange throttled concurrent connections. For example, Microsoft 365 will only allow 10 concurrent connections per admin account.
- Mailbox Provisioning. A mailbox was provisioned shortly before initiating migration, and the mailbox wasn't fully available. For example, Microsoft 365 will frequently return this error if a mailbox is submitted immediately after provisioning, due to data center replication delays.
- Excessive Server Load. The target server was under an excessive load, and so started returning this error. For example, Microsoft 365 servers usually experience high load at specific times such as Fridays (evenings) or Mondays (mornings).
We recommend trying the following:
- If using administrative credentials, using impersonation will likely resolve the issue.
- In many cases, replication or server load issues are resolved simply by waiting a few minutes.
- Check the admin account:
- Make sure it is a global admin (Microsoft 365).
- Make sure it has a mailbox that can be logged in to (use OWA).
- Consider granting explicit permissions to all mailboxes.
- Check throttling limits:
- Decrease the number of simultaneous migrations. The default Exchange 2010 limit is 10.
- Consider creating more than one connector, each using a different admin account.