Krogulec, a polish blogger from http://www.dobreprogramy.pl/Krogulec, showed a simple trick to do it.
Before you start, you'll need two things
- Developer mode (Settings - Security - Developer Mode). This will allow you to use N9's Terminal.
- Nano (or any other text editor for Nokia N9)
- Open Fenix Mail's configuration file. To do that type in Terminal the following (mind you this is case-sensitive): nano /home/user/.config/Nokia/Fenix.conf
- Add the following line in Fenix.conf file (## is the the desired size value, e.g. 50, see the photo)
Note that this value should not exceed the limit imposed by the mail provider - for example, 25MB limit on gmail.com. Save the changed file pressing Ctrl + O, Enter and Ctrl + X to exit. Close the Terminal, restart your phone and you're done!