hi-ho.ne.jp で試した方法です。

プログラム

hi-ho.py

#! /usr/bin/python
#
#	hi-ho.py
#
#						Jun/26/2023	
# --------------------------------------------------------------------
import	os
import	sys
import	socket
from dotenv import load_dotenv
import	email
from email.mime.text import MIMEText
from email.utils import formatdate
# --------------------------------------------------------------------
from send_starttls import send_starttls_proc
# --------------------------------------------------------------------
sys.stderr.write ("*** 開始 ***\n")
dotenv_path = '.env'
load_dotenv(dotenv_path)
mail = {}
mail['server'] = os.environ.get("SERVER")
mail['port'] = os.environ.get("PORT")
mail['usr'] = os.environ.get("USR")
mail['password'] = os.environ.get("PASSWORD")
mail['from'] = os.environ.get("FROM")
mail['to'] = os.environ.get("TO")


contents = 'Hello, Good Afternoon! on Jun/26/2023 from Hi-ho\n'
contents += 'Jun/26/2023 PM 13:34\n'
contents += 'こんにちは。\n'
contents += ' ' + socket.gethostname ()

message = MIMEText (
	contents,
	'plain',
)

message['Subject'] = 'Hello Jun/26/2023 from Hi-ho'
message['From'] = mail['from']
message['To'] = mail['to']
message['Date'] = formatdate ()

send_starttls_proc (mail,message)
#
sys.stderr.write ("*** 終了 ***\n")
# --------------------------------------------------------------------

send_starttls.py

# -*- coding: utf-8 -*-
#
#	send_starttls.py
#
#						Jul/05/2020
# --------------------------------------------------------------------
import	sys
import	smtplib
# --------------------------------------------------------------------
# [6-4]:
def send_starttls_proc (mail,message):
	sys.stderr.write("*** send_starttls *** start ***\n")
	ss = smtplib.SMTP (mail['server'],mail['port'])
	ss.ehlo ()
	ss.starttls ()
	ss.ehlo ()
	ss.login (mail['usr'],mail['password'])
	ss.sendmail (
		mail['from'],
		[mail['to']],
		message.as_string (),
		)
	ss.close ()
#
	sys.stderr.write("*** send_starttls *** end ***\n")
# --------------------------------------------------------------------

.env

SERVER = 'hi-ho.mose-mail.jp'
PORT = 587
USR = '****@hi-ho.ne.jp'
PASSWORD = '****'
FROM = '****@hi-ho.ne.jp'
TO = 'sample@example.com'

実行結果

$ ./hi-ho.py 
*** 開始 ***
*** send_starttls *** start ***
*** send_starttls *** end ***
*** 終了 ***

確認したバージョン

$ python --version
Python 3.13.7