We replace several computers running Windows XP Pro and Outlook Express to Windows 7 Pro and Outlook 2010.
The official way to migrate emails in this case is to install Outlook 2010 on the same computer as Outlook Express, and perform an import. I'm not aware of another method. This allows emails, contacts, and even server settings (addresses, usernames and passwords) to be imported, but we are only interested into emails and contacts.
On some computers, only a small fraction of the emails are migrated.
We start with, say, 5000 emails, and we have about 500 after migration. The emails are lost according to date: during 4 or 6 months, not a single email is kept.
The last one I saw this afternoon had about 600 emails into the "Sent" folder. From January 1st to august 21 (today). After being migrated, only January 1st to April 13 were available in Outlook 2010. Other folders were impacted in a similar way, but with varying dates.
We tested with Outlook 2007 and exact same dates.
We tested deleting 50% emails before migration, exact same dates.
We tested with Thunderbird and not a single email was lost (individual count for each folder).
We have this problem on about 1 out of every 10 computers. All these problems are from computers with lots of emails (more than approximately 5000). But not every big mailbox leads to this problem.
How can we transfer emails from Outlook Express to Outlook 2010 (or 2007, we can take care of the final step up to 2010) ?