Preparing Outlook for first use

I've been using Outlook 2007 for quite a while already but today when I started Outlook, I got the following notification;
"Preparing Outlook for first use."

Then it shows a dialog where it appears to be importing by emails which is taking forever.

What exactly is going on here and why does Outlook state that it hasn't been used before?

This can be caused by various updates for Outlook and is normal behavior, although the timing can be quite annoying when you really need to access your mailbox.

New data structure for performance

Outlook 2007 Service Pack 2 (SP2) introduced a new data structure for the pst- and ost-file which allowed for improved performance. This change to the data structure is also required for several updates when you are still running Outlook 2007 with Service Pack 1 (SP1) or when you make the switch to Outlook 2010 from a previous version of Outlook.

After you apply such an update, Outlook will first update the data structure of your connected pst- and ost-files before opening. Depending on the size of your data files, this process could take 2 minutes but also several hours (when you have a really large mailbox and several large pst-files connected as well).


The wording of the dialog might have been chosen a bit poorly though as it has nothing to do with Outlook being used for the first time. Also, the dialog gives you the impression that something is copied or imported instead of something being updated.

This dialog can be quite confusing… and annoying…

No way to cancel or skip…

There is no way to cancel the process either or access Outlook without having the file format being updated first. If you are using Exchange, you could consider connecting via OWA instead if you really need to directly access your emails.

Another way to go would be to locate your ost-file and rename it to .old. This will force a rebuild of the cache of Outlook, which means it will download a copy of all the mails on the server again to your local computer. While this takes time as well, it could be faster than the conversion process.

This trick does not work for pst-files though so when you are using a POP3 account or have additional pst-files connected to your mail profile with Exchange, then you’d still have to sit out the conversion process.

… but it is worth the wait!

The good thing about it, is that it does provide a great performance benefit afterwards when you are working with a large mailbox or have a large amount of emails in a single folder. Also, changes to the data structure of Outlook’s pst- and ost-files is not something the Outlook development team takes on lightly, so it is not like this will happen again soon after another update.

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