When using a smart client, the end-users cannot launch an email dialogue window but they can send automated mail if they choose to.
Some users require SMTP protocols to be setup for automated services that send out emails because they do not install MS Outlook on servers. Occasionally, the SMTP settings are accidentally included when packaging up the smart client. Check the smart client package's email settings for SMTP settings, if there are SMTP settings in the smart client package remove them and redeploy the smart client. This will ensure that the smart-clients use the default Outlook plugin.