Manual:$wgEnableUserEmailBlacklist

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Email settings: $wgEnableUserEmailBlacklist
Set to true to enable user-to-user email blacklist.
Introduced in version:1.30.0 (Gerrit change 374361; git #Ifa26153)
Removed in version:1.37.0 (Gerrit change 680806; git #4dae3b1a)
Allowed values:(boolean)
Default value:false