I think that we posted messages last year in the talk pages of users
without an email address.
Although I can't find evidence of that in the archives, so maybe we only
talked about doing so.
Anyway, I developed a tool for listing WLM participants without an e-mail:
http://toolserver.org/~platonides/wlm/nomail.php
It lists users without an authenticated e-mail. I recommend that each
local organization team
prepares a boilerplate in their local language and posts to the talk
pages of the users that
participated with photos of their country (if they decide sending such
messages).
If when you are going to notify a user you notice that you have the
"E-mail this user" link on
their talk page, then they *do* have an email set, it was a false
positive from my tool
(I saw some instances, either due to replication lag or the toolserver
copy is desynchronized).
There will also be some false negatives, for people that do have an
email address set in their
preferences but have explicitely disabled receiving emails from other
users (which is what we
really care about). Hopefully, there will be few of those.
Regards