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 your own mail address
account user@domain.name

# 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 your own mail address
account default: user@domain.name

# 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.

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