Mail sending issue, asp.net

Im having issue with mail sending In web.config file

<mailSettings>
    <smtp from="xxxx@companyname.com">
    <network host="mail.authsmtp.com" port="25" userName="xxxx@companyname.com" password="****" defaultCredentials="false"/>
            </smtp>
        </mailSettings>
</system.net>

I used mail sending code to send mail

but im getting exception as, The server response was: 5.0.0 Your email system must authenticate before sending mail:XM_ERR:xxx.xxx.xxx.xxx(my ip addr)

Please let me know how to solve this issue.

Thank you

Do you want to use credentials from web.config file?

If yes, than change defaultSettings to true.

If not, than you must supply valid credentials in code.