setting a category for mail object

Hello,

i have been trying to use the object api for setting a category on a selected mail.

After some research, my question is: Is this even possible with the object api and if so, how? :)

( i am using a C3PO and the ClientState.Selected Messages. I then convert the SelectedMessages into a MessageList and so on. I'm not sure if this is the correct way)


Thanks in Advance!