[Evolution] How to add a function button on tool bar

[Dario Lesca <d lesca solinos it>]

On Evolution 3.24.4 (3.24.4-1.fc26), how to add another function button
on tool bar, like "trash" or "mark as spam" or other few features for
which a button is provided?

I would add a button for "mark as read" some block of message, without
use menu bar or right click.

It is possible do that ?

Many thanks

-- 
Dario Lesca
(inviato dal mio Linux Fedora 26 Workstation)