python3 email robot to be run periodically

mailbot.py

#! /usr/bin/env python3
# mailbot.py is an email robot
#
# It connects to an IMAP mail server, looks at all of the messages,
# picks out the ones that have just a U or u in the Subject: header,
# scans them for all of the image attachments, saves them to a
# web-server accessible uploads folder, and replies to the message
# through the SMTP server with the URL(s) of the uploaded photos.
# The images are renamed to a UUID. Any message that got a reply is
# then deleted from the IMAP server.
#
# This script was designed to be run periodically on the server.
#
# Configurtion variables below

SERVER = 'example.com'
PORT = 143
USER = 'user@example.com'
PASSWORD = 'password of user'
DIRECTORY = '/server/static/upload/directory/'
SERVER_USER = 'newfileusername'
SERVER_GROUP = 'newfileusergroup'
URL_BASE = 'https://example.com/upload/base/url/'
MAIL_FROM = 'Super Mailbot <mailbot@example.com>'

import ssl, imaplib, email
import mimetypes
import uuid
from os import path
import os, pwd, grp
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
import smtplib

mimetypes.init()

server = imaplib.IMAP4(SERVER,port=PORT)
context = ssl.create_default_context()
typ, data = server.starttls(ssl_context=context)
if typ == 'OK':
	#print('TLS sesion started')
	pass
else:
	raise Exception('TLS session failed to start')

typ, data = server.login(USER,PASSWORD)
#print('%s'%(data[0]))

typ, data = server.select()
#print('%d messages in the INBOX'%(int(data[0])))

class Image:
	pass

typ, data = server.search(None, 'ALL')
for num in data[0].split():
	typ, data = server.fetch(num, '(RFC822)')
	message = email.message_from_bytes(data[0][1])
	images = []
	if message['Subject'].lower() == 'u':
		for part in message.walk():
			#print(part.get_content_type())
			if part.get_content_maintype() == 'image':
				#print(part.get_filename())
				filename_extension = '.'+part.get_filename().split('.')[-1].lower()
				possible_extensions = mimetypes.guess_all_extensions(part.get_content_type(), strict=True)
				if filename_extension not in possible_extensions:
					filename_extension = possible_extensions[0];
				filename = str(uuid.uuid4()) + filename_extension
				full_filename = path.join(DIRECTORY, filename)
				full_url = URL_BASE + filename
				img = Image()
				img.original_filename = part.get_filename()
				img.filename = filename
				img.full_filename = full_filename
				img.url = full_url
				#print(filename)
				part_data = part.get_payload(decode=True)
				with open(full_filename,'wb') as f:
					f.write(part_data)
				uid = pwd.getpwnam(SERVER_USER).pw_uid
				gid = grp.getgrnam(SERVER_GROUP).gr_gid
				os.chown(full_filename,uid,gid)
				os.chmod(full_filename, 0o664)
				images.append(img)
		if len(images):
			reply = MIMEMultipart()
			reply['From'] = MAIL_FROM
			reply['Subject'] = 'RE: ' + message.get('Subject','')
			if 'Reply-To' in message.keys():
				reply['To'] = message['Reply-To']
			else:
				reply['To'] = message['From']
			if 'Message-Id' in message.keys():
				reply['In-Reply-To'] = message['Message-Id']
			if len(images) > 1:
				content_string = 'Your images have been uploaded to the following urls:\n\n'
			else:
				content_string = 'Your image has been uploaded to the following url:\n\n'
			for image in images:
				content_string += '\t"%s": %s\n'%(image.original_filename,image.url)
			content = MIMEText(content_string)
			reply.attach(content)
			#print(reply)
			smtp_server = smtplib.SMTP(SERVER)
			smtp_server.starttls()
			smtp_server.login(USER, PASSWORD)
			smtp_server.send_message(reply)
			smtp_server.quit()
			server.store(num,'+FLAGS',r'\Deleted')

server.expunge()

typ, data = server.close()
#print('%s'%(data[0]))

typ, data = server.logout()
#print('%s'%(data[0]))