problem with outlook

hello, i need a help, i have a server configured with ISPconfig, my problem is when i configure the outlook or outlook express, i send mail to other mail of the same server and no problem, when a send the mail to gmail o other domain the outlook do not send, and show me the text: Server Response: `554 5.7.1 SSL server error 554 error number: 0x800CCC79, please help me.

 

Enable "SMTP requires authentication" in account settings.

 

thanks for answer:
I have a other question: if i don't need SMTP authentication, how i disconnect that property, i have Ubuntu 8.04 and ISP config.
Thanks for all.

 

You should use SMTP authentication because without that your mail sever can be used for SPAM.

 

ok, but who i disconnect the authentication SMTP.
Thanks for all.

 

I'm sorry, but I don't understand the question?