BOFH solution
I worked for a Govt organization that sensibly locked down email clients to text-only mode. Outlook was deliberately crippled to prevent one from enabling anything but plain text.
BOFH part: If you tried to enable html, or send html, or click on a link, you were sent to a "reeducation camp". In this IT Siberia, people are forced to watch presentations on email safety. Powerpoint shows designed to crush the spirit and create unthinking compliance. One viewgraph every 30s for an hour. The quiz at the end requires a perfect score. Imperfect score? Re-do the training.