Send Mass Email with Python

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import smtplib
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.header import Header
from email.utils import formataddr

# Import TEXT only File as Body
t = open('textmsg.txt', 'r')
tmsgfile = t.read()
# Import HTML only File as Body
h = open('htmlmsg.txt', 'r')
hmsgfile = h.read()
# Import E-Mail addresses from file. Separate mail@ddress per line
addr_f = open('mails.txt', 'r')
addr_list = []

for line in addr_f:
    addr_list.append(str((line).replace("\n","")))
#addr_list.sort()
print addr_list
print "\nE-Mails count : ", len(addr_list)

# Pick Up email recipient from list and send email to address
counter = 1
for mail in addr_list:
    from_mail = formataddr((str(Header('www.mysite.sk', 'utf-8')), 'info@mysite.sk'))
    to_mail = mail

    msg = MIMEMultipart('alternative')
    msg['Content-Type'] = "text/html; charset=utf-8"
    msg['Subject'] = Header('MySubject', 'utf-8')
    msg['From'] = from_mail
    msg['To'] = to_mail

    text = tmsgfile
    html = hmsgfile
    part1 = MIMEText(text, 'plain', "utf-8")
    part2 = MIMEText(html, 'html', "utf-8")

    msg.attach(part1)
    msg.attach(part2)

    s = smtplib.SMTP('smtp.server.sk:25')
    s.starttls()
    s.login('info@mysite.sk','MyPass')
    s.sendmail(from_mail, to_mail, msg.as_string())

    print "\n", counter, "Message sent to :", mail
    counter += 1

s.quit()
print "\nFinish"