Finally with this simply line (DEFAULT = /home/myusername/mail/INBOX)
that Tom said the filters are working fine for the main account
I made a copy of .forward and .procmailrc files to
/home/myaccount/mail/my_virtual_mail_account1/ too but the filters
aren't working for this account (ofcourse i change the paths with the
right one)
Is it possible to invoke the virtual mail accounts which are under
/home/myaccount/mail/my_virtual_mail_account with my main filters of my
home account?