Created attachment 7225 Replace missing icon by freedestop compliant icon Adwaita icon theme doesn't have internet-mail image, I suggest to replace this one by emblem-mail icon. Patch fixes this issue.
Yup, that makes sense. I'm in favour of that change. For reference: https://specifications.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html#names (Guess after this is fixed I need to actually add the icon in elementary-xfce too...)
Olivier Duchateau referenced this bugreport in commit 29474fe37267266e785511808ff2586bd196600c Use freedesktop.org mail icon name compliant (Bug 13711) https://git.xfce.org/xfce/exo/commit?id=29474fe37267266e785511808ff2586bd196600c
Thanks for the patch. Applied above.
The icon still not compliant since emblem is not supposed to be used for menus but instead for the filemanager only. I'ld preffer keep the old and add add fallback, but I think why not aplication-mail and ship a icon like the standard say in case of need?