Outlook Express in Windows XP Pro

My Outlook Express sent and received mail with no problem from 2004 until March of 2012.  Suddenly at that time Outlook Express stopped sending, replying, & forwarding all email.  It continues to receive fine but gives me an error message every time I try to send, reply or forward.  If I go directly to the email site on the web, I am able to send.  No settings have been purposefully changed.  Could some part of Norton 360 be interferring with this?

My Outlook Express sent and received mail with no problem from 2004 until March of 2012.  Suddenly at that time Outlook Express stopped sending, replying, & forwarding all email.  It continues to receive fine but gives me an error message every time I try to send, reply or forward.  If I go directly to the email site on the web, I am able to send.  No settings have been purposefully changed.  Could some part of Norton 360 be interferring with this?