At the time being communication through email is less important than 10 years ago. Facebook, Whatsapp, Telegram, Slack, etc there is a feeling like old good email has less importance now for a meaning of communication. However, there is a field where this way of communication still being very important, when not the only way of communication. I'm talking about servers here.
For example, when ssh server detects break-in attempt it will try to send an email notification (or at least it could be configured in this way), or when some crontab-job fails, it also will try to send an email. But there is a problem, sometimes installing full-fledged MTA is counter-productive. Think about Raspberry Pi, if you install Postfix there it will be eating precious (and limited) resources of the machine itself. And we are not talking about the effort you will need to invest in an administration of the email server.
For myself, I found a much simpler solution called msmtp. According to their website:
msmtp is an SMTP client.
In the default mode, it transmits a mail to an SMTP server (for example at a free mail provider) which takes care of further delivery. To use this program with your mail user agent (MUA), create a configuration file with your mail account(s) and tell your MUA to call msmtp instead of /usr/sbin/sendmail.
In other words, you may connect to any SMTP server and send messages to any directions as if they were users on localhost. I will be using gmail.com for this.
First of all, you will need to install it. Surprisingly for me, the version contained within Ubuntu repository is pretty old. However, you may build the latest version, this is not covered in this article.
$ sudo apt-get update
$ sudo apt-get install msmtp msmtp-mta
Then I created a new email address at Gmail just to receive notifications from servers.
Configuration is pretty straightforward.
# File: /etc/msmtprc
# Set default values for all following accounts.
defaults
auth on
tls on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile /var/log/msmtp.log
# Gmail
account gmail
host smtp.gmail.com
port 587
# If you're relaying through Gmail you can put here whatever you want. It's going to be ovewritten by your gmail's address.
from xandnotify@gmail.com
user xandnotify
# For me this password is not SO secret, but if you want to hide it there are many options.
password myverysecretpassword
# Set a default account
account default : gmail
aliases /etc/aliases
Please note the /etc/aliases file. We will need to use it later.
I'm not sure about the user which is going to execute msmtp command, so the log file should be created beforehand with proper permissions.
$ sudo touch /var/log/msmtp.log
$ sudo chmod 666 /var/log/msmtp.log
Now you can test the whole setup with the following command:
$ echo "Hello there" | msmtp --debug your@email.com
If everything is OK you should receive an email at your@email.com. If not, try to see the debug output and figure out what went wrong.
For mail command to work you will need to put the following in /etc/mail.rc. Please note that in order to have mail utility you will need to install mailutils package which, unfortunately, on Ubuntu also includes Postfix server.
# File: /etc/mail.rc
set sendmail="/usr/bin/msmtp -t"
You can test that mail works with following command:
$ echo "This is a message body" | mail -s "Hello there from mail command line" xand@xand.es
When crontab fails to execute some command it sends an email message. In order to perform the operation, it uses sendmail executable. If you remember, in the beginning, I also installed msmtp-mta package. Doing so also creates a link /usr/sbin/sendmail to /usr/bin/msmtp. This way crontab does not need any additional configuration.
The problem here is that crontab always sends a message to a local user. I mean, if I log in as admin user and create a crontab job for this user the email will be sent to admin at localhost. It can be fixed using the following approaches.
This file defines email aliases for user. For example:
# File: /etc/aliases
root: admin@myserver.com, supervisor@myserver.com
default: catch-all@myserver.com
Given this configuration, all emails which go to root@localhost will also be sent to admin@myserver.com and supervisor@myserver.com. Also, all messages to unknown (non-existent) users will be sent to catch-all@myserver.com.
Crontab offers a more elegant way of sending emails. In the beginning of the crontab file, you can edit it with crontab -e, declare MAILTO variable. Like this:
MAILTO="xand@xand.es"
* * * * * /tmp/aaa.sh
That's it. Your comments are welcome.