Disabling sending form templates with the email forms must be configured.

InfoPath allows users to attach form templates when sending e-mail forms. If users are able to open form templates included with e-mail forms, rather than using a cached version that is previously published, an attacker could send a malicious form template with the e-mail form in an attempt to gain access to sensitive information. Note: The form template is only opened directly if the form opens with a restricted security level. Otherwise the attachment is actually a link to the published location.