I wanted to send emails to more than one user, so I wrote a sending method, and then read the file in a loop. I wanted the recipient to see that the only recipient in the email was myself, but the recipients still showed multiple recipients in the list. The first recipient in the file sees one, and the second recipient sees the first two as if they were appended to the list, but when to_addr is printed out in the call, there is only one address, not Multiple addresses.
I sent it later, and commented msg['To'] to avoid displaying the recipients, but I wanted to understand why multiple recipients were displayed.
Please help me analyze it.

#!/usr/bin/python
# -*- coding: UTF-8 -*-
import smtplib
import os
import socket
import commands
from email.mime.text import MIMEText
from email.header import Header
def send(a,b):
    user = 'xxxx'
    from_addr = 'xxxx@xxxx.com'
    password = '***********;'
    smtp_server = 'smtp.xxxx.com'
    to_addr = b
    print "##############"+to_addr
    msg['To'] = Header(to_addr, 'utf-8').encode()
    server = smtplib.SMTP(smtp_server, 25)
    server.set_debuglevel(1)
    server.login(user, password)
    print '**************'+to_addr
    server.sendmail(from_addr, to_addr, a.as_string())
    server.close()
if __name__ == '__main__':
            msg = MIMEText('内容文字内容文字', 'plain', 'utf-8')
            msg['Subject'] = Header(u'我是标题', 'utf-8').encode()
            file = open("sample.txt")
            #lines=file.readlines()
            for i in file:
                print i 
                print "##"
                q=send(msg,i)