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

InfoPath allows users to attach form templates when sending email forms. If users are able to open form templates included with email forms, rather than using a cached version that is previously published, an attacker could send a malicious form template with the email 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.