Some times :
- I may make a typo in the subject and send it
- A sender might send an empty or irrelevant subject
- A message subject might arrive with modifications from antispam (take *** SPAM *** tags for example).
In those cases, I like to amend the subject to keep consistency and cleanliness. I am able to do this in eM Client, and I think it was also possible through an add-on the days I was using Thunderbird.
Allow message subject editing when single or double clicking on it.