Disabling of email forms from the Full Trust Security Zone must be configured.

InfoPath provides three security levels for form templates: Restricted, Domain, and Full Trust. The security levels determine whether a form template can access data on other domains, or access files and settings on your computer. Fully trusted forms have a Full Trust security level, and can access files and settings on users' computers. The form template for these forms must be digitally signed with a trusted root certificate, or installed on users' computers. By default, InfoPath can open email forms with full trust. If an attacker designs and sends a dangerous fully trusted email form, it could affect users' computers or give the attacker access to sensitive information.