two factors will with gmail.
you can go into google my account settingsl and have it generate you a unique password for both k9 and thunderbird to setup your email on those two apps and any other devices that needs access to your google account. So instead of using your regular password, it uses a complex auto-generated password which is needed to access your google/gmail account.
Only issue with it is sometimes with certain older apps it doesn't work that well but beyond that, it at least one security measure.
I have the google authenicator which i use with gmail on my android samsung phone which works and also you can setup so if you don't want to use the authenicator, you can do text messaging to your phone directly for vertification.
Edited by MasterNe0, 13 October 2016 - 10:47 AM.