If you do not specific an email address your email software, verify your email address and that your "Reply to:" setting contains your valid email address.
Outlook Express
Open Outlook Express.
Click Tools on the menu and select Accounts.
Click the Mail tab.
Select your mail account and click the Properties button.
On the General tab, be sure the email address you entered in the E-mail address: field is valid, is spelled correctly and does not contain spaces or commas.
Click OK and OK again. Note: Unless you would like to use a different email address than the one specified in the Email Address: field, you do not need to fill in the "Reply address:" field.
Send a test message to yourself to see if you receive the message and can reply to the message successfully.