Outlook is flaging my local messages to spam

[kazabeDELETE]

Hi.

At the last week some users in my office are having some little
problem with Outlook. Apparently some local mails has been flaged to
spam, and saved in the spam folder.

We have the spam controls in the mailserver, blocking all the spam.
so we dont use local spam policies, because all are centralized in the
server.

How can i understand why Outlook are doing that?

Thanks in advance