The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was'. Subject 'isp', Account: 'mail.bigpond.com', Server: 'mail.bigpond.com', Protocol: SMTP, Server Response: '550 Invalid recipient: <>', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79

Is bigpond.com your new ISP or your old one?Do you connect via a mobile internet USB modem?Is the Secure Password Authentication (SPA) option unchecked?Is your anti-virus application configured to scan incoming/outgoing mail?To how many recipients were you attempting to send this message with the subject "isp" ?Note: Outlook Express has nothing to do with Internet Explorer. You should be posting your OE questions in this forum: http://social.answers.microsoft.com/Forums/en-US/xpnetwork/threads ~Robear Dyer (PA Bear) ~ MS MVP (IE, Mail, Security, Windows & Update Services) since 2002 ~ Disclaimer: MS MVPs neither represent nor work for Microsoft