It's not a secret that KMAIL has the ability to set customs templates per folder. In the custom template you can use commands like %OTIME, %OTIMELONG etc.
The question is - if it's possible to modify headers from the commands?
If not then why not to implement commands like %SUBJECT="My Subject% %FROM="foo@test.com" %BCC
then when message is created from a certain folder SUBJECT is automatically set to My Subject, FROM to foo@test.com
it could be a time saver.

I know that it's possible to use identities but identities don't give that kind of flexibility. Why not allowing changing message headers from the templates themselves?

I'm not sure the templating was designed with this specific use case. As far as I can tell, it's mainly meant for static changes.

einar wrote:I'm not sure the templating was designed with this specific use case. As far as I can tell, it's mainly meant for static changes.

May be it's a good idea to add this feature to the wish-list. It could be useful.

In that case, please open a wishlist request on bugs.kde.org (or perhaps go to the KDE Brainstorm first).

You could use a draft to achieve something similar, and filters can be used modify headers on otgoing mails, if you can identify your mails with the available options.