[imp] nowhere to select encoding method when compose

[yahsuan at Lab400-51.cc.ntu.edu.tw]

my horde app version is:
horde                     4.0.1   stable
imp                       5.0.1   stable
ingo                      2.0.1   stable
turba                     3.0.1   stable

and my php version is PHP 5.3.3

When I compose a new message, there is nowhere to select encoding method.
Is it by design?

Thanks in advance.