The move to CSD and buttons in the header bar has broken toolbar button customisation via .ui files
Previously copying .ui files from /usr/share/evolution to ~/.config/evolution/ui and editing them would allow customisation of visible buttons on the toolbars, but this doesn't seem to work at all now.
This is especially useful on mobile devices, where horizontal real estate is limited. I realise that Geary exists and has an adaptive interface, but unfortunately, its mail handling (at least on IMAP) is full of bugs and not as mature/reliable as Evolution's.
Previously, removing unnecessary tooolbar buttons would be enough to have a usable Evolution interface when scaled to a mobile screen.