This issue has been resolved. Pre-Stage migrations are now operational. Thank you for your patience.
Posted May 28, 2018 - 05:20 PDT
Our developers have identified the issue causing non-mail item types to migrate during a pre-stage migration, and are developing a fix to resolve the issue. We will update this as soon as that fix is deployed.
Posted May 27, 2018 - 10:54 PDT
We've identified an issue where Pre-Stage migrations are migrating more than just Mail item types. If you wish to submit a migration for only migrating mail item types, please use a Full Migration Pass while deselecting all other item types except mail before submitting. To filter by date in a Full Migration, please use the date filtering found in Edit Project > Advanced Options.