I don’t want my server to be an SMTP-server but I do want it to be able to send me e-mails. Hence, Postfix is overkill and I settled with msmtp and Gmail.

Installation

Installation is straightforward. msmtp is available in Debian’s repositories.

$ sudo apt update && sudo apt install msmtp msmtp-mta

On my system, this installs ca-certificates libgsasl7 libntlm0 msmtp openssl.

Preparation

msmtp is not a full-blown SMTP relay. We want it to send e-mails through Gmail’s SMTP-servers. While you can go the long way and go for OAUTH2 as explained in the Arch Linux wiki, I went for the short version with app passwords. you can read more about this on the Google help pages.

First, make sure you enabled 2-factor authentication for your Gmail account.

Next, generate an app password: https://security.google.com/settings/security/apppasswords. It looks like this: fgoelxqlduacnryt. Write it down or temporarily save it to a file because you’ll only see this once. You’ll have to create a new password then.

Options don’t matter much but can be handy for later identification.

You’ll only see this password once.

Possibly, unblock with the captcha: https://accounts.google.com/DisplayUnlockCaptcha

Configuration

In my case I only set up one account, the default. I don’t need individual users to be able to send their own e-mails.

The configuration resides in one file:

sudo nano /etc/msmtprc

# Copy the contents below
account        default
auth           on
tls            on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile        /var/log/msmtp

# gmail
host           smtp.gmail.com
port           587
from           youraccount@gmail.com
user           youraccount
password       yourapppassword

# Syslog logging with facility LOG_MAIL instead of the default LOG_USER
syslog LOG_MAIL

# Aliases file
aliases /etc/aliases

In the aliases file the system looks for the address where to send the e-mails to. Hence, we populate the file.

$ sudo nano /etc/aliases

# Copy the contents below
# Bug: recursive lookup doesn't seem to work in current Debian version
# Setting every e-mailaddress explicitely
mailer-daemon: postmaster
postmaster: root
nobody: root
hostmaster: root
...
root: youraccount@gmail.com

Test and finalize!

Send an email:

$ echo "Hello this is sending email using msmtp" | msmtp bertmelis@gmail.com

There might be a problem with the setup. Somehow msmtp doesn’t create its log file.

$ sudo touch /var/log/msmtp
$ sudo chown msmtp:msmtp /var/log/msmtp
$ sudo chmod g+w /var/log/msmtp

Now it works:

echo "hello there username." | msmtp -a default username@domain.com

One more thing. The app password is stored in plain text. So we should limit access to this file.

# limit access
sudo chmod 660 /etc/msmtprc
# create a group called 'msmtp' not needed, probably already there
# sudo groupadd msmtp
# repeat the following for each group member
sudo usermod -aG msmtp username

We’re all done!

Mailbox image by anSICHThoch3 from Pixabay