404 not found for links in email when sharing a page or sending page notification / Custom message is not included in email

Email notifications for sharing pages / notifiying users (via right sidebar) do not work as expected.

Link https://we.riseup.net/code/FIEqlG6fr9 leads to 404 not found
Custom message entered in text field "Include a custom message " is not included in Email.

See also #129 (closed)

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