If you remigrate calendar data, you might encounter problems. For example, if you migrated a recurring event, made a change to it in Google Apps, and then remigrated that same event, the change you made in Google Apps would be lost.
If you need to remigrate contact and calendar data for some reason, you need to first delete the data you migrated originally, and then run a new migration.
When planning your migration, take the following considerations into account.
The e-mail migration tools do not migrate your organizations distribution lists / groups into Google Apps.
The e-mail migration tools do migrate e-mails sent to groups or distribution lists. You will need to ensure these groups are provisioned into Google Apps before users start to use Google Apps to ensure properly e-mail flow when users reply to messages sent to these groups.
When a domain is configured for dual delivery at the email gateway, mail between users within the same organization will not routed to external gateways and dual delivered. If you are running in this configuration you may want to consider also migrating e-mail to Google Apps for the period of time you have dual delivery enabled.
If there are errors or problems with a user migration you may choose to remigrate all data for that user. Doing so will not duplicate existing email content already in the mailbox.
If your organization is migrating from one domain name to another within Google Apps (for example, from mydomain.com to otherdomain.com), be sure the proper e-mail aliasing is in place to ensure the migrated data is properly reflected within Google Calendar.
To avoid migration issues, make sure you provision all users in Google Apps before migrating calendars. For details, see “Avoid Calendar issues” on page 18.