Following the move of mail operations to a new server, Wikimedia e-mails were temporarily blacklisted by SpamCop following alleged e-mails received by spamtrap addresses. As a result, and due to the small possibility of Wikimedia e-mail services being used to send spam mail, brion enabled e-mail confirmation on all Wikimedia wikis.
The setting disables e-mail communication by default, forcing all users to send a confirmation e-mail in order to re-enable it. This is done to ensure that e-mail addresses given are in fact that of actual users. A user must first visit Special:Confirmemail, and send a confirmation e-mail to their address. Then, they must open the e-mail and click the confirmation link inside the e-mail to confirm the address. After this is finished, e-mail communication is possible between users.
E-mail addresses are still not required, but if added, will not function unless a confirmation is sent. The confirmation must only be performed once per account, though users with multiple accounts on different wikis must confirm each separate account if desired.
SpamCop unblocked Wikimedia's mail server shortly after the announcement, though due to the possibility of being re-listed, the e-mail system will remain in effect permanently.