Always when I open Geary it automatically maximize.
I looked into settings in dconf tools
org.yorba.geary window-maximize is not checked.
Anybody who knows how to fix this?
It's not a bug, it's a feature ;)
elementary OS automatically maximizes every starting window that is bigger than 70% of your screen size. You can turn off this behaviour by running the following command in your terminal:
gsettings set org.gnome.mutter auto-maximize false
BTW: It will be disabled by default in the next release of elementary OS.