I'm not a fan of Outlook Express so I've not used it on my current machine so it's basically 'clean'
This is how I created an account.
(replace example.com with true domain)
Using Tools>account then add > mail.
firstname.lastname@example.org (make sure this exists as a mail user)
Incoming is POP3
Remember password box is ticked
Leave SPA box unticked
Now go back to tools>account and select the account you have just created and click properties. Leave 'General' as is . Click 'servers' tab and tick box under Outgoing mail server. click the 'setting' button next to the box you just ticked and select 'Use same settings as incoming...'
Click on apply and then OK.
Close Internet Accounts box.
Click the small arrow to the right of send/recv and select the new account you just created from the drop down to download email.
To send email click the 'Create mail' button.
In the composing box if there have been other accounts created make sure the correct user is selected in the from drop-down.
P.S. Introduce your client to 'Mozilla Thunderbird'