Messages not received dependent on email address

Hi, I've found that when people fill in my online contact form, sometimes the message isn't transmitted. What's odd is that the message is stored in the database but not sent to me. If someone uses a gmail address or hotmail, I dont get the confirmation email. If I use the same message but change the email address, the message comes through fine! Im confused! -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://groups.google.com/group/recaptcha. For more options, visit https://groups.google.com/groups/opt_out.