Sending signed email [closed]

Is this a good way to send a signed email message? It seems to me that a public key is a little too large to send as a email header. Should I be including the signature and key as a header field, or should I be sending it within the message body?

What are some ways that I could improve this script to make its usage more practical for sending email?

import smtplib
from email.MIMEMultipart import MIMEMultipart
from email.MIMEText import MIMEText

from Crypto.Signature import PKCS1_v1_5
from Crypto.Hash import SHA256
from Crypto.PublicKey import RSA

FROMADDR = "[email protected]"
TOADDRS = ["[email protected]"]
LOGIN = ""
PASSWORD = ""
body = "hello world"

key = RSA.importKey(open('/mnt/external_sd/keys/private.asc').read())
h = SHA256.new(body)
signer = PKCS1_v1_5.new(key)
signature = signer.sign(h).encode("base64")

msg = MIMEMultipart()
msg["X-signature"]=signature
msg["X-public-key"]=open("/mnt/external_sd/keys/public.asc").read().encode("base64")
msg['From'] = "[email protected]"
msg['To'] = "[email protected]"
msg['Subject'] = 'sign test'
msg.attach(MIMEText(body, 'plain'))

server = smtplib.SMTP_SSL('smtp.example.net', 465)
server.set_debuglevel(1)
server.ehlo()
server.login(LOGIN, PASSWORD)
server.sendmail(FROMADDR, TOADDRS, msg.as_string())
server.quit()