Hi Sean,
Yes, you can configure E-mail format via
CMS Site Manager -> Settings -> System -> E-mails -> General section -> E-mail formatOr if you want to send E-mails via API as mentioned before:
CMS.EmailEngine.EmailMessage em = new CMS.EmailEngine.EmailMessage();
em.EmailFormat = CMS.EmailEngine.EmailFormatEnum.PlainText;
Best regards,
Martin Danko