For those who are still using the old "Outlook Express" there might be a chance that you are going to encounter an error saying that it cannot open a message from the outbox folder.
There's actually a simple fix to that problem. All you need to do is close Outlook, locate the outbox.dbx on your computer and delete it or rename it.
After deleting the outbox.dbx just open Outlook again and the error will be magically fixed.
How does the problem happen?
It's a case of corruption. The outbox.dbx might have corrupted that's why Outlook is unable to read the message on the folder.
What is the purpose of outbox folder?
Outbox folder acts as a storage for all unsent email. All unsent email will appear on the outbox folder. Once an email is sent Outlook will transfer the email from outbox folder to the sent folder.