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The EXTERNAL.EXE program that functions as a Message Transfer Agent (MTA)
for version 3.2 of Microsoft Mail for PC Networks will continue to fully function while it displays one of the additional information screens. These screens are initiated by pressing either the F1 key (Help Screen), the F2
key (Dispatch Mail Status), or F3 key (External Status). While one of these
screens is displayed, EXTERNAL.EXE will still continue to transfer mail
between postoffices and answer incoming asynchronous calls.
The EXTERNAL.EXE program provides the Administrator with five separate
display screens. The first is the startup/copyright screen displayed when
EXTERNAL.EXE is initialized. The second is the main logging screen
displayed by default, and it shows the normal logging information. The
other three screens are the F1, F2, and F3 screens that display the help
screen, the Dispatch Mail Status, and the External Mail Status,
The previous version of EXTERNAL.EXE (versions 3.0 and earlier) were
designed strictly for the MS-DOS environment. Therefore, the function that
modified the F1, F2, or F3 display screen sat in a polling loop, waiting
for the user to press the ESC key to continue processing. For these
versions of EXTERNAL.EXE, while one of these screens was being displayed,
EXTERNAL.EXE could not deliver mail or answer incoming asynchronous calls.
The newer versions of EXTERNAL.EXE (versions 3.2 and later) were designed
for a multiprocessing environment. In particular, the EXTERNAL.EXE process
was designed to be event driven. Even though the F1, F2, and F3 display
screens have not changed in content or functionality, EXTERNAL.EXE now
continues to fully function while any of these screens is being displayed.
Versions 3.2 and later of EXTERNAL.EXE now use a foreground/background
screen mechanism to take care of the proper display dynamics. When one
screen is being displayed, EXTERNAL.EXE simply writes any information bound
for the standard, logging screen directly to the video screen memory
background buffer. This allows the user to instantly switch from one of the
F1, F2, or F3 screens back to the logging screen and instantly see the
correct logging information.