This guide shows how to install and configure msmtp on Kubuntu/Ubuntu so Bash scripts (including cron jobs) can send email alerts reliably.

It is written for a typical use case:

  • You have a Bash monitoring script (e.g., uptime checks)
  • You want to send email via Gmail SMTP using an App Password
  • You want it to work both manually and from cron

1) Install msmtp and certificates

Update packages and install required components:

sudo apt update
sudo apt install -y msmtp msmtp-mta ca-certificates

Verify msmtp is installed:

msmtp --version

2) Create the msmtp configuration file

msmtp reads configuration from ~/.msmtprc (per-user). Create it:

nano ~/.msmtprc

Paste this Gmail-based configuration and update your email and app password:

defaults
auth           on
tls            on
tls_starttls   on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile        ~/.msmtp.log

account gmail
host smtp.gmail.com
port 587
from [email protected]
user [email protected]
password YOUR_16_CHAR_APP_PASSWORD

account default : gmail

Notes:

  • Use SMTP 587 + STARTTLS (recommended)
  • Do not use your normal Gmail password; use an App Password
  • The logfile helps with troubleshooting (~/.msmtp.log)

3) Lock down file permissions

msmtp will refuse to use an insecure config file. Set permissions:

chmod 600 ~/.msmtprc

Confirm:

ls -l ~/.msmtprc

You should see something like:

-rw------- 1 youruser youruser ... .msmtprc

4) Create a Gmail App Password

Gmail SMTP typically requires:

  • 2-Step Verification enabled
  • An App Password (16 characters)

Steps (high level):

  1. Go to Google Account Security settings
  2. Enable 2-Step Verification
  3. Open App passwords
  4. Create an app password for Mail
  5. Copy the 16-character key and paste it into ~/.msmtprc

5) Test msmtp manually (must pass before cron)

Send a test email:

echo -e "To: [email protected]\nFrom: [email protected]\nSubject: msmtp test\n\nHello from msmtp" | msmtp [email protected]

If you receive it, msmtp is working.

If it fails, check the log:

cat ~/.msmtp.log

6) Make sure cron can find msmtp (PATH + HOME)

Cron runs with a minimal environment. The two most common causes of “works manually but not via cron” are:

  • PATH missing /usr/bin
  • HOME not set to your user home

Check msmtp location:

which msmtp

Expected output:

/usr/bin/msmtp

In your crontab (crontab -e), include:

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOME=/home/youruser

Then call your script with an absolute path.

Example cron line:

* * * * * /home/youruser/scripts/uptimerbt/check_once.sh >> /home/youruser/scripts/uptimerbt/uptime_monitor.log 2>&1

7) Optional: Test sending from a cron-like environment

Run the command with a minimal env to simulate cron:

env -i HOME="$HOME" PATH="/usr/bin:/bin" bash -lc 'echo -e "To: [email protected]\nFrom: [email protected]\nSubject: cron-like test\n\nHello" | msmtp [email protected]'

8) Common errors and fixes

msmtp: cannot locate trust file

Install certificates:

sudo apt install -y ca-certificates

msmtp: authentication failed

  • Make sure you used an App Password
  • Confirm 2-Step Verification is enabled
  • Re-check from, user, and password entries

Works manually but not in cron

  • Add PATH and HOME lines in crontab (see above)
  • Use absolute paths in cron jobs
  • Confirm the cron job runs as the same user who owns ~/.msmtprc

If you prefer not to store the password directly in ~/.msmtprc, you can use passwordeval with a secret manager (e.g., pass). That’s more secure, but slightly more complex. For a personal laptop, an app password with chmod 600 is typically acceptable.

Quick checklist

  • sudo apt install msmtp msmtp-mta ca-certificates
  • ~/.msmtprc created and correct
  • chmod 600 ~/.msmtprc
  • App Password used (not your Gmail password)
  • Manual test email works
  • Cron has PATH and HOME set (if needed)