If you mean you want your PC to spell check the emails before they are showing on Outlook Express?
As far as I am aware you cannot spell check emails as they come in.
When you send a email,Outlook Express offers you the facility of spell check,this is not on offer when an email arrives in Outlook.
The only way I can see you doing this is to copy/paste the email into a Word document and spell check it from there,of course this may not be what you want.as the quanitiy of emails may be too large.
There may be a programme that you can download to do this,but I don't know of one.
Hopefully someone in Technology might be able to give you better news?