Configure mail transport agent on Raspbian with external SMTP server

I want to get email notifications for actions on my Raspberry Pi using Raspbian. You could setup a separate mail server for that action but that seems to be a little bit overkill.

msmtp is a mail transfer agent which uses a configured smtp server for email transfer. This allows you to send emails via a configured smtp server (in my case from my webspace provider All-Inkl.com – by creating a new account using this link you’ll support the costs for running this blog).

Upgrade your raspbian:

sudo apt-get update && sudo apt-get upgrade

Install msmtp:

sudo apt-get install msmtp msmtp-mta mailutils

Get the location of the configuration files:

> msmtp --version
msmtp version 1.6.6
Platform: arm-unknown-linux-gnueabihf
TLS/SSL library: GnuTLS
Authentication library: GNU SASL
Supported authentication methods:
plain scram-sha-1 external gssapi cram-md5 digest-md5 login ntlm
IDN support: enabled
NLS: enabled, LOCALEDIR is /usr/share/locale
Keyring support: none
System configuration file name: /etc/msmtprc
User configuration file name: /home/pi/.msmtprc

Copyright (C) 2016 Martin Lambers and others.
This is free software.  You may redistribute copies of it under the terms of
the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
There is NO WARRANTY, to the extent permitted by law.

Configure the system configuration:

sudo vi /etc/msmtprc

The content of my configuration file (note the necessary changes for servers and email addresses):

# Set default values for all following accounts.
defaults

# Use the mail submission port 587 instead of the SMTP port 25.
port 465

# Always use TLS.
tls on
tls_starttls off

# Set a list of trusted CAs for TLS. The default is to use system settings, but
# you can select your own file.
tls_trust_file /etc/ssl/certs/ca-certificates.crt

# If you select your own file, you should also use the tls_crl_file command to
# check for revoked certificates, but unfortunately getting revocation lists and
# keeping them up to date is not straightforward.
#tls_crl_file ~/.tls-crls

# Mail account
# TODO: Use the users username, e.g. root for system and pi for your raspbian user
account root

# Host name of the SMTP server
# TODO: Use the host of your own mail account
host <your Username provided by KAS>.kasserver.com

# As an alternative to tls_trust_file/tls_crl_file, you can use tls_fingerprint
# to pin a single certificate. You have to update the fingerprint when the
# server certificate changes, but an attacker cannot trick you into accepting
# a fraudulent certificate. Get the fingerprint with
# $ msmtp --serverinfo --tls --tls-certcheck=off --host=smtp.freemail.example
#tls_fingerprint 00:11:22:33:44:55:66:77:88:99:AA:BB:CC:DD:EE:FF:00:11:22:33

# Envelope-from address
# TODO: Use your own mail address
from user@domain.name

# Authentication. The password is given using one of five methods, see below.
auth on

# TODO: Use your own user name fpr the mail account
user <The username of the email account you use for sending emails>

# Password method 1: Add the password to the system keyring, and let msmtp get
# it automatically. To set the keyring password using Gnome's libsecret:
# $ secret-tool store --label=msmtp \
#   host smtp.freemail.example \
#   service smtp \
#   user joe.smith

# Password method 2: Store the password in an encrypted file, and tell msmtp
# which command to use to decrypt it. This is usually used with GnuPG, as in
# this example. Usually gpg-agent will ask once for the decryption password.
#passwordeval gpg2 --no-tty -q -d ~/.msmtp-password.gpg

# Password method 3: Store the password directly in this file. Usually it is not
# a good idea to store passwords in plain text files. If you do it anyway, at
# least make sure that this file can only be read by yourself.
# TODO: Use the password of your own mail account
password <The password of the email account you use for sending emails>

# Password method 4: Store the password in ~/.netrc. This method is probably not
# relevant anymore.

# Password method 5: Do not specify a password. Msmtp will then prompt you for
# it. This means you need to be able to type into a terminal when msmtp runs.

# Set a default account
# TODO: Use the same account you've configured under account, e.g. root or pi
account default: root

# Map local users to mail addresses (for crontab)
aliases /etc/aliases

This file contains a username and password. Therefore limit its access to only root:

sudo chmod 600 /etc/msmtprc

Duplicate the config file to ~/.msmtprc if you want to provide email configuration for your user as well. Don’t forget to update the accounts accordingly.

Now configure the recipients for your systems users by setting the recipients in /etc/aliases. Make sure, that you don’t have trailing spaces behind the email addresses:

root: user@domain.name
default: user@domain.name

Let your computer now that msmtp should be used as replacement for sendmail by adding this content to /etc/mail.rc

set sendmail="/usr/bin/msmtp -t"

Test your configuration by sending an email from the terminal:

echo "Content of your mail" | mail -s "Subject" user@domain.name