Mailslot

From HandWiki

Mailslot is a one-way interprocess communication mechanism, available on the Microsoft Windows operating system that allows communication between processes locally. Mailslots also supported communication over a network. The use of Mailslots is generally simpler than named pipes or sockets when a relatively small number of relatively short messages is expected to be transmitted, such as for example infrequent state-change messages, or as part of a peer-discovery protocol. Up until Windows 11 24H2, the Mailslot mechanism also allowed for short message broadcasts ("datagrams") to all listening computers across a given network domain.[1][2] The mechanism originated in LAN Manager, a component of OS/2, an operating system co-developed by IBM and Microsoft.[3] Mailslots were discontinued in Windows 11 24H2.[4][5]

Features

Mailslots function as a server-client interface. A server can create a Mailslot, and a client could write to it by name. Only the server can read the mailslot, as such mailslots represented a one-way communication mechanism. A server-client interface could consist of two processes communicating locally or across a network. Mailslots operated over the RPC protocol and worked across all computers in the same network domain. Mailslots offered no confirmation that a message had been received. Mailslots were generally a good choice when one client process need to broadcast a message to multiple server processes.[1][2]

Uses

The most widely known use of the Mailslot IPC mechanism was the Windows Messenger service that was part of the Windows NT-line of products, including Windows XP. The Messenger Service, not to be confused with the MSN Messenger internet chat service, was essentially a Mailslot server that waited for a message to arrive. When a message arrived, it was displayed in a popup onscreen. The NET SEND command was therefore a type of Mailslot client, because it wrote to specified mailslots on a network.

A number of programs also used Mailslots to communicate. Generally these were amateur chat clients and other such programs . Commercial programs usually preferred pipes or sockets.

Mailslots were implemented as files in a mailslot file system (MSFS). Examples of Mailslots included:

  • MAILSLOT\Messngr - Microsoft NET SEND Protocol
  • MAILSLOT\Browse - Microsoft Browser Protocol
  • MAILSLOT\Alerter
  • MAILSLOT\53cb31a0\UnimodemNotifyTSP
  • MAILSLOT\HydraLsServer - Microsoft Terminal Services Licensing
  • MAILSLOT\CheyenneDS - CA BrightStor Discovery Service

References

  1. ↑ 1.0 1.1 Brain, Marshall; Ron Reeves (2000). Win32 System Services: The Heart of Windows 98 and Windows 2000. Prentice Hall PTR. pp. 230–243. ISBN 0130225576. https://archive.org/details/win32systemservi00mars/page/230/. 
  2. ↑ 2.0 2.1 Mitchell, Stan (1997). Inside the Windows 95 File System. O'Reilly. pp. 292–295. ISBN 156592200X. https://archive.org/details/bitsavers_microsoftwidetheWindows95FileSystem1997_40878940/page/292/. 
  3. ↑ Plateau, Brigitte, ed (2013). Handbook on Parallel and Distributed Processing. Springer Berlin Heidelberg. p. 249. ISBN 3662043033. https://www.google.com/books/edition/Handbook_on_Parallel_and_Distributed_Pro/CBnpCAAAQBAJ?hl=en&gbpv=1&dq=%22mailslot%22+%22windows%22+%22os/2%22&pg=PA249&printsec=frontcover. 
  4. ↑ Burt, Jeff (March 13, 2023). "Windows 11 puts 'disgusting' Remote Mailslots protocol out of its misery". The Register. Archived from the original on June 5, 2026. https://web.archive.org/web/20260605125552/https://www.theregister.com/software/2023/03/13/used-in-windows-for-decades-remote-mailslots-are-done/672083. 
  5. ↑ Jawad, Usama (March 10, 2023). "Microsoft is getting rid of the Remote Mailslot legacy protocol in Windows 11 soon". Neowin. Archived from the original on June 15, 2025. https://web.archive.org/web/20250615183222/https://www.neowin.net/news/microsoft-is-getting-rid-of-the-remote-mailslot-legacy-protocol-in-windows-11-soon/. 



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