Get an email upon failed systemd services

Only by chance I noticed a failed systemd service. It’s a rather crucial
service, namely my backup.
I’ve decided to get an email for such circumstances.
The solution consists of three parts:

  1. The actual backup service unit
  2. An unit status mail service
  3. An python email script

On failure, the actual service triggers the email service which in turn triggers
the email script.

The %h in the highlighted line, refers to the User home directory as per systemd.unit

~/.config/systemd/user/backup.service 
[Service]
Type=oneshot
ExecStart=/usr/bin/sh $h/bin/backup.sh

[Unit]
Description=Homefolder backup
OnFailure=unit-status-mail@%n.service

/etc/systemd/system/unit-status-mail@.service 
[Unit]
Description=Unit Status Mailer Service
After=network.target

[Service]
Type=simple
ExecStart=/home/ra/bin/unit-status-mail.py %I

~/bin/unit-status-mail.py 
#!/bin/python
import smtplib
import argparse
from subprocess import Popen, PIPE
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText

parser = argparse.ArgumentParser()
parser.add_argument("unit")
args = parser.parse_args()
unit = args.unit

usr = 'foo@bar.com'
pwd = 'secretpassword'
host ='mail.host.com'
port = 465

msg = MIMEMultipart()
msg['From'] = usr
msg['To'] = usr
msg['Subject'] = f'Failed: {unit}'
cmd=f'systemctl status --user --full {unit}'
# Be aware of security issues when using shell=True
stdout = Popen(cmd, shell=True, stdout=PIPE)\
    .stdout.read().decode('utf-8')
msg.attach(MIMEText(stdout))

with smtplib.SMTP_SSL(host,port) as mail_server:
    mail_server.ehlo()
    mail_server.login(usr, pwd)
    mail_server.sendmail(usr, usr, msg.as_string())

I wrote this article while metaphorically standing on the shoulders of Laeffe
Furthermore I made slight changes according to this question