Q4.0.12: Customisation of VM not covered in the manual, or here.

giacomo boffi writes:

The meta-answer is to look into the file vm-vars.el, in the vm directory of the lisp library.

vm-vars.el contains, initializes and carefully describes, with examples of usage, the plethora of user options that fully control VM’s behavior.

Enter vm-vars, forward-search for toolbar, find the variables that control the toolbar placement, appearance, existence, copy to your init.el or .vm and modify according to the detailed instructions.

The above also applies to all the various features of VM: search for some keywords, maybe the first you conjure isn’t appropriate, find the appropriate variables, copy and experiment.