Manual:$wgSysopEmailBans

Access: $wgSysopEmailBans
Allow sysops to ban users from accessing Special:Emailuser.
Introduced in version:1.11.0 (r22816)
Deprecated in version:1.34.0 (Gerrit change 534701; git #3a2c7d1b)
Removed in version:1.35.0 (Gerrit change 542315; git #I72e2574)
Allowed values:(boolean)
Default value:true

Details

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If set to true, a checkbox is enabled in Special:Block that allows sysops to block a user from accessing Special:Emailuser to send email to other users.