Installing the SAP Stand Alone Gateway 
Prerequisites
You need administrator authorization for the SAP Internet Mail Gateway server.
You have assigned a system name <SID> for the R/3 stand alone gateway.

The same restrictions apply for the SID as for a normal R/3 installation (three alphanumeric characters, first character cannot be a number). Please note that the following names are not permitted:
ADD, ALL, AND, ANY, ASC, COM, DBA, END, EPS, FOR, INT, KEY, LOG, MON, NOT, OFF, RAW, ROW, SAP, SET, SGA, SHO, SID, UID.
You can for example select SIG as the system name (provided this does not clash with a system that is already installed).
The installation program is located on your computer (in Windows NT in the subdirectory
\NT\i386\ ) or on the R/3 Presentation CD, which is part of the standard system of the R/3 System.Procedure
1. Unix and Windows NT:
Execute the file R3gwinst.exe.
A wizard guides you through the installation process.

Set the number of CUA users to 0, as only R/3®R/3 connections are used.
If the installation is unsuccessful and the Service SAP <SID> is already installed, you must remove the service manually using the command ntscmgr remove SAP<SID>_<ID> before the next installation attempt.
OS/400:
Alternatively use program R3SETUP as described in the installation guide R/3 Installation on IBM AS/400.
rdisp/max_gateways = 1
rdisp/workdir = d:\usr\sap\SIG\G00\work
rdisp/TRACE = 1
gw/max_sys = 30
gw/max_shm_req = 10
gw/max_wp = 0
gw/remsh = remsh
gw/keep_process = 1
gw/rem_start = REMOTE_SHELL