SMTP Authentication problem

[nandar]

Hi,

I configured "SMTP authorization is required" under Plesk >Server >Mail. But, in outlook, I can send emails without checking "My outgoing mail server requires authentication". As far as I know, if I turn on "SMTP authentication" in plesk, I need to set up "my mail server requires authentication" in outlook. Otherwise, I should not be able to send emails. Can anyone explain me what do I miss here?

Also, from outlook, I can send emails from non-existence email address to local addresses.
for example,
sender : [email protected] (non-existence email)
receiver : [email protected]

So, it means anybody who knows my SMTP server can send spam emails to all the email addresses in my server.

Can anybody help me out to solve this problem? Thanks.