You might get the next error message:

Message Could Not Be Opened From Outbox Folder, Account: mail.yourdomain.com. MailAccount,Server: smtp.myisp.co.uk, Protocol:SMTP,Interface:25,Protect(SSL):No, Error Number:0x800420CB

Solution
The common reason for this difficulty is really a corrupted Outbox.dbx file. To repair it:

ClickTools
SelectAccounts
Click the Mail tab
Select a duplicate email account, and then click Remove. Keep carrying this out until all duplicated accounts have already been removed.
ClickClose

Still having difficulties with this particular error message? Take to renaming the Outbox.dbx file. Please notice that this will permanently delete any messages still in the outbox.

CloseOutlook Express
Right-click theStartbutton on your own desktop
ClickFindorSearch
Look for theOutbox.dbxfile
Right-click the file, click Delete, then click Yes
Start Outlook Express, then take to again.