Office 365 Pre-Migration Preparations
Step 1. Review Your Deleted Items Folder
Items in the “Deleted Items” folder will only be retained for 30 days following the migration. The 30-day retention policy only applies to the “Deleted Items” folder. If you wish to retain mail items found in the “Deleted Items” folder please move them to a different folder.
Step 2. Identify Large Emails/Attachments
Large emails or emails with large attachments may slow down or prohibit the migration process. You can prevent problems from arising by checking your inbox and other folders for messages larger then 35MB by searching for “messagesize:>34 MB” in Outlook and OWA clients
Step 3. Make a backup of your signature and rules
Signatures and rules do not migrate to Office 365, so they will need to be backed up and imported or recreated. Make a backup of your signature and rules by following the instructions found here: