I'm not sure if this is an Adobe issue or Thunderbird. Problem (exists on Co-worker's computer): Have a pdf form with a MAILTO(+email address) button to send off in email. When I click the mailto link, 3 things happen (or don't) The email does get sent to the person the button specifies, a new email window does not open up, and there is no record in the sent folder of this message getting sent. I am using this exact copy of the form on my machine as well. When I click the mailto link, I get a popup of a new message window that I can edit the subject/body of the email and then send the message, and the email does go into my sent folder. What I've tried so far: Verified that Thunderbird is my default client through Internet settings. Also verified that MAILTO links are pointed to Thunderbird. Also verified that Adobe Reader is sending the mailto link to my default client. I'm stumped... any help would be greatly appreciated.