Try these links to the Elgg documentation:
http://docs.elgg.org/wiki/No_emails_%28including_validation_emails%29_are_being_sent
http://docs.elgg.org/wiki/Missing_emails
Via the admin section you can also activate accounts that have not been activated by the users yet via the "Unvalidated users" option in the side menu.
info@elgg.org
Security issues should be reported to security@elgg.org!
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