I've guessed you mention about autosave feature like SublimeText, but I tried TexAdept and found only Save session at the File Menu, it's not autosave, just save the sessions by hand
Sylpheed is lack of good HTML render engine. That's why I still not change to Claws or Sylpheed because its. This time is 2017, and I don't want to read and imagining about the figure that was appeared as text description in email.