After install and configure KMail 16.12.2-1 on an Arch Linux system (kernel 4.9.11-1 x86_64) with KDE Plasma 5.9.2, KDE Frameworks 5.31.0,
when I go to manage the identity I find my identity created, and more than 1,000 identity 'Unnamed' created automatically.
I tried using these instructions http://userbase.kde.org/KMail/FAQs_Hint%20...%20_migration and clean up everything else, but I still
have over a 1000 "Unnamed" identities!
How do I delete all these identities, or clear/delete file (manually it is too long a procedure)?
Thanks in advance for any suggestions.

After editing file ~ /.config/emailidentities as suggest in other 3d, and run KMail, all 'Unnamed' identities have been eliminated.