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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) ?

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@HopelessN00b: thanks for the edition. I see you are familiar with that and your english is way much better than mine. – Gregory MOUSSAT Aug 21 '12 at 16:04
up vote 2 down vote accepted

The only cure I know is to use Windows Live Mail to do the job:
1. install Windows Live Mail on the old computer
2. from Windows Live Mail, import messages from Outlook Express
3. from Windows Live Mail, export messages to Outlook 2007/2010

No problem with very big mailboxes.

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The first thing I'd suggest is exporting from Outlook Express, and importing the resulting mailfile into Outlook. For some reason this seems to work better than just trying to import directly into Outlook.

If that doesn't help, then I'd point out that version 6 of Outlook Express (which came with XP, I think) has a maximum mailbox size of 2GB. My guess would be that the accounts that aren't migrating all the emails are running into that limit - either there's another mailfile that you need to import that got created after the mailbox reached the 2GB limit, or the mailbox kept growing and got corrupted.

If there's just a second mailfile you need to import as well, that's easy enough - do it.

If the mailfiles have become corrupted so that Outlook can't import them directly, since Thunderbird can, you might want to look into exporting the database from Thunderbird to a format Outlook can read, and get the mailboxes into Outlook that way.

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