SUMMARY The html messages sent do not respect the font size chosen in the new message editor. STEPS TO REPRODUCE 1. write new message, set font size of your html message to 12px 2. send it and open in Outlook 2016. Font not use the size defined by sender (12px). OBSERVED RESULT Font in Outlook 2016 is 10px EXPECTED RESULT Email editor respect font size defined on write new message. SOFTWARE/OS VERSIONS Windows: - macOS: - Linux/KDE Plasma: KDE Neon/5.15 (available in About System) KDE Plasma Version: 5.15.4 KDE Frameworks Version: 5.57.0 Qt Version: 5.12.0 ADDITIONAL INFORMATION Workaround: open Kde system configuration, goto fonts, set default font size to 12. Write new html mail and send it. Open in Outlook 2016 and the mail have correcte font size. I deduce that kmail uses the default size of the system and not the one defined in the message editor when sending the message.