Guest Email goes wrong

When guest fill the form and send it via website,in the mailbox it’s appear as guest-email-id@mydomain.com (not guest-email-id@guest-domain.com),but in the content of the email,submitted e-mail address was just fine (appear as it input by the guest),what happen? could you give me any info or suggestion for this matter?

Regards,
Copz

Solved it,the web host support says,I have to modified the sendmail script,what I’ve done is editing the reservation.class.php,and it works.