All you can do is ask them to whitelist you by adding you to their address book or contact list -- also known as "approved senders". Most email programs allow you to mark emails as not junk or spam so that future emails do not get misidentified as spam.
You'll also want to check that your domain isn't blacklisted. If you just bought the domain, it could have a poor history that you'll need to address.
Judith "Do one thing every day that scares you." ~ Eleanor Roosevelt