What ISP/mail provider are you with (i.e., the bit after the @ in your e-mail address)?
I have never known Outlook Express to require a DNS/IP address.
If you have the POP3 bit (normally pop3.<serviceprovider>.co.uk) then substitute SMTP for POP3:-
e.g., if your e-mail is from blueyonder:-
These are the norm and will usually be on the website of your mail provider.