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Set up a 'buddy-list' to quickly see which of your friends are currently online
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Entering your email address will not leave you open to 'spam', as you can choose to hide your email address in your personal control panel, and messages sent to you via email do not reveal your address to the sender in any case. (To verify this, you can try sending an email message to another user.)
The administrator has configured the forum to send you the final part of the registration process by email, so ensure that the email address you provide is valid and working.