The TRANS_MAILSLOT_WRITE transaction subcommand was introduced in the LAN Manager 1.0 dialect. It is used to write a message to a mailslot.

The subcommand code for a TRANS_MAILSLOT_WRITE is 0x0001, which is identical to the subcommand code for TRANS_SET_NMPIPE_STATE. This is permitted because transaction subcommand codes are not global; they are interpreted relative to the resource being accessed.

There are no mailslot operations that are defined as part of the CIFS protocol. Mailslots are not accessed over SMB sessions (although the Mailslot sub-protocol defines a mechanism for doing so). As a result, mailslot operations are documented separately. For more information on the Remote Mailslot Protocol, see [MS-MAIL] and [MSLOT].

Windows clients do not send TRANS_MAILSLOT_WRITE commands via CIFS sessions. Related protocols, such as [MS-BRWS], send Class 2 mailslot messages as NetBIOS datagrams. TRANS_MAILSLOT_WRITE commands carrying Class 2 messages do not require responses. See [MS-MAIL].