Many web hosting companies require that the email address you are sending the emails to match the domain you are using. For instance, if your domain is TRAVELAGENT.COM, the emails sent by your contact form must go to
someone@TRAVELAGENT.COM. If you try to send them to
someone@gmail.com they won't go through. I just re-did my web site and dealt with this same issue. I created an email account just for the contact form (using my web site domain) and then set that email account up to forward to my gmail account.
Hope this helps.
kathy