Why do my mail keep going to the spam box

[asmiA]

Hi
Whenever i send somebody email that email i sent from my system get in the user's spam folder.My friend inform me with gmail. I am using opera i also tried with Firefox but same thing can any one help me ?
thank you

[timon]

SpamBox checks your incoming messages as they come in to the ITCS e-mail servers.algorithms to compare the content of the messages.SpamBox is very accurate, but it will occasionally make a mistake when figuring out which messages are spam but for you check your spam settings in mail.

itd.umich.edu

[Trio]

Changed SPF setting also mainly spam depends on your domain name, your servers IP/hostname so will check the headers and where it is sending from, or check with your host for any spam blacklisting which may appear over the server.