The unsubscribe URL is used within the `mass_mailing` module,
e.g. in `_get_unsubscribe_url` & `send_get_email_dict`.
Basically, there is the possibility to add the unsubscription
link in the mass mailings while having only
`mass_mailing` installed.
But, the unsubscription route is defined within
the module `website_mass_mailing`.
Therefore, if you added the unsubscription link
within your mailings while not having
`website_mass_mailing` installed, trying
to follow the unsubscription link leaded to
a `404 Not Found` page.
We therefore define the route within `mass_mailing`
directly, which does the basic stuff (the basic
unsubscribe and confirmation), and override this route
in `website_mass_mailing`, where the advanced stuff is done
(the mailing lists list unsubscription and the better
looking page).
opw-669425
Denis Ledoux