So, if you are fairly confident about the character string that marks the end of each mail message in this file format, then the perl code that would step through a file one message at a time would be pretty simple:

{
    open( IN, "pegasus.file" ) or die $!;

    local $/ = "\x1a";  # change the input record separator

    while (<IN>)    # $_ now contains one whole message,
    {               #   up to and including \x1a
       # do what you want with the message
       # including, if you like:
 
       @lines = split /\n/;   # work on lines

       # or you could strip off the pegasus header stuff
       # and treat the remainder as if it were vanilla email
       # (just like you'd get with common unix mail tools)
    }
}
# record separator now reverts back to default
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