It's unclear what you're trying to achieve.
New site email address: change in the admin backend on the "Configure" - "Settings" - "Basic Settings" page when logged in as admin.
New email address for a user account: when logged in as this user go to the user settings ("Settings" link in the topbar menu, i.e. on Elgg 1.8 in the upper right corner of any page) and change the email address.
info@elgg.org
Security issues should be reported to security@elgg.org!
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