Qmail - vpopmail virtual domains on single IP

Hello all,

i have problem with my qmail.
I added in my qmail control files: rcpthosts
my virtualdomains
virtual1.com
virtual2.com
and in my virtualdomains file:
virtual1.com:virtual1.com
virtual2.com:virtual2.com

i setup my dns that:

for vritual1.com:

1D IN MX 10 mail.first.net.

and for virtual2.com:

1D IN MX 10 mail.first.net.

mail.first.net is my domain on server and MX for my domain first.net

The problem is that when i send email to yahoo and other sites,
my emails from virtual domains marked as spam (bulk mail)
any body have idea where is my mistake ?

Regards,
Condor