Spam problem

[franiuu]

Hi there.

I have a problem with sending emails from my roundcube. I have a Ubuntu server with Plesk 12.5 on it. When I am sending an email using Roundcube every of them is marked as a spam (every mailbox I sended to). When I am using Horde this problem doesn't exist. But... I realy prefer roundcube so if anyone of you knows how repair it please help me

P.S. Sorry for my bad English

[SKaero]

Make sure you've setup SMTP in Roundcube.