> i am using qmail on redhat linux.i have one default domain of linux and
> other 2 domain as virtual domains through vpopmail.
You asked exactly the same question under the subject "authentication of
default and virtual domain users" a couple of days ago, and I posted an
answer, which you didn't comment.
Please don't double-post the same question, especially not if somebody
already answered it. If my answer didn't solve your problem, tell us
what exactly happened.