When migrating mailboxes from Groupwise to Exchange how does the size of the Exchange mailbox change when everything has been migrated over?
When migrating mailboxes from Groupwise to Exchange sometimes the size can increase up to 3 times in size; however, this is not always the case. This number depends on the geometry and type of data. Some data converts to larger messages while others convert to smaller messages.
Calendar data may decrease in size during migration because of the different ways that Groupwise and Exchange stores appointments.
Rich text messages may get bigger since the conversion from Groupwise RTF to MS RTF cause the data size to increase.
Results will be different in different environments and the results will be different for each mailbox. Unfortunately there is no accurate way to determine what you will experience during your migration.