Is it possible for Pegasus to be loaded with Windows, minimized, sitting in the background, waiting for formatted text files from a DOS program, that will automatically "see" the file, and send the text email to the email address provided. No pictures or attachments.

Pegasus Mail can be loaded at startup, minimized.

Messages created in Pegasus Mail can be queued for sending so I suspect that you could produce a file that would meet final form message requirements and write it to a Pegasus Mail mailbox directory. Unfortunately, Pegasus Mail would not automatically detect and send it. Messages created in Pegasus Mail can be sent immediately upon saving, or they can be queued, with the send being triggered manually or by the next POP3 check for new mail. Unlike Mercury, the only configurable mechanism for sending queued messages with Pegasus Mail is a POP3 mail check, at least not AFAIK.

Would have to do testing, but I did this as a test using Pegasus Command line option.
Created a regular text file in this case was in Programs subdirectory when created.
I'm using Pegasus under Linux, so might be different under windows.
Found I had to use full path to file, an in linux required double backslashes, but preview here is only showing single??
wine WINPM-32.EXE -T mikes@guam.net -F c:\PMAIL\Programs\testcmdline -S "Test Command LINE"

created XBH0NIXW.PMW queued message in Mail Directory.

mikes@guam.net, Test Command LINE
SY:0
I8:0
TO:mikes@guam.net
SU:Test Command LINE
RE:mikes@guam.net
EN:0
CS:1
RC:0
DC:0
UR:0
SS:0
SG:0
MI:0
ID:<Default>
FI:c:\PMAIL\Programs\testcmdline
ME:0
MF:0
TX:0
EX:0
FL:0

Test command line message

Opened Pegasus, and the queued message was there, and send sent message.
Not sure what happens if Pegasus is open and command line option done.
Would think that if it is setup to autocheck/send mail it would after time, send message.

Did another test, but it is more complex.
Created an outgoing queued message, and it created two files.
285 Aug 2 07:20 GO12R4AZ.PMW
738 Aug 2 07:20 GO12R4AZ.PNX
PNX file is RTF formatted.

{\rtf1\sstecf29000\ansi\deflang1033\ftnbj\uc1\deff0 
{\fonttbl{\f0 \froman DejaVu Serif;}}
{\colortbl ;\red255\green255\blue255 ;\red0\green0\blue0 ;}
{\stylesheet{\f0\fs24 Normal;}{\cs1 Default Paragraph Font;}{\s2\snext0\f0\fs24\b0\ul0\i0\cf2\fi0\li0\ri0\sb0\sa0\sl0 body;}}
{\*\revtbl{Unknown;}}
\paperw12240\paperh15840\margl2010\margr2010\margt1440\margb1440\headery720\footery720\nogrowautofit\deftab680\formshade\nofeaturethrottle1\useltbaln1\dntblnsbdb\fet4\aendnotes\aftnnrlc\pgbrdrhead\pgbrdrfoot 
\sectd\pgwsxn12240\pghsxn15840\guttersxn0\marglsxn2010\margrsxn2010\margtsxn1440\margbsxn1440\headery720\footery720\sbkpage\pgncont\pgndec 
\plain\plain\f0\fs24\ql\plain\f0\fs24 message body??\par 
\plain\f0\fs24\par 
}

PMW file is

Note: First byte is a character 01 that doesn't seem to show in preview.

mikes@guam.net <mike, test que message 2           

SY:0
I8:1
TO:mikes@guam.net <mikes@guam.net>
SU:test que message 2
RE:mikes@guam.net
EN:0
CS:1
RC:1
DC:1
UR:0
SS:0
SG:0
MI:1
CE:UTF-8
ID:<Default>
ME:0
MF:0
TX:0
EX:0
HP:0
ED:1600 504
RX:GO12R4AZ.PNX
FL:0

So, might be a way?