Sagi,

From your logs it looks as if you have your domain (mydomain.com) listed in the "Excluded FROM Emails" or in the "Excluded Domains / IPs". Please note that unless there is a very specific need to do that, you in general will want to avoid placing your own domain in your whitelists. If not, you will see exactly what is happening now, which is spammers faking your domain name that bypass all rules when sending you emails. You should only have your domain (mydomain.com) listed under the "Local Domains" whitelist. The Local Domains tell SpamFilter which emails it should receive emails for, while still applying all other filtering rules.