Enable remote mailslots
This DWORD value controls whether the SMB client processes remote mailslots through MUP.
since 0.9.8.11
Purpose
Show registry keys (1)
HKLM\Software\Policies\Microsoft\Windows\NetworkProvider\EnableMailslots
This DWORD value controls whether the SMB client processes remote mailslots through MUP. The value 0, as set by Setup Foundry, disables this functionality. Remote mailslot requests are therefore no longer passed through the SMB client redirector.
Mailslots provide one-way interprocess communication and can carry short messages to a specific computer or to multiple computers in a domain. This setting affects network access to remote mailslots; it does not disable local mailslots.
Notes
Security
The Remote Mailslot protocol has no built-in authentication or authorization mechanisms and is classified by Microsoft as obsolete, unreliable, and insecure. Setting the value to 0 removes this communication path through the SMB client redirector. This reduces exposure to applications and protocols that might otherwise exchange unauthenticated remote mailslot messages.
Possible side effects
Legacy applications and protocols that depend on remote mailslots through the SMB client can no longer send or process those messages. Such requests may fail with ERROR_REMOTE_MAILSLOTS_DEPRECATED. Components that also rely on SMB 1 or legacy Computer Browser functionality are the most likely to be affected.
Notes
This value belongs to the client-side Enable remote mailslots policy under Lanman Workstation. It is distinct from the similarly named server-side policy, which uses a different registry key.
Microsoft documents this policy for Windows 11, version 24H2, and later. Remote Mailslot is disabled by default on those systems. A value of 0 means disabled; a value of 1 means enabled.
Microsoft documentation
Microsoft Learn: Policy CSP – LanmanWorkstation
Microsoft Learn: SMB security hardening in Windows Server and Windows Client