#!/usr/bin/env python3.6

import sys

fn = sys.argv[1]
out = sys.argv[2]
with open(fn, "rb") as fd:
    lines = fd.read().split(b"\n")

def dup(lines, what):
    idx = []
    met = False
    for i, line in enumerate(lines):
        if line == "":
            break
        if met:
            if line.startswith(b" "):
                idx.append(i)
                continue
            else:
                met = False
        if line.startswith(what):
            if len(idx) == 0:
                idx.append(i)
                met = True
            else:
                return [l for n, l in enumerate(lines) if n not in idx]
    return lines

lines = dup(lines, b"To")
lines = dup(lines, b"From")
lines = dup(lines, b"Subject")
with open(out, "wb") as fd:
    fd.write(b"\n".join(lines))