Simplest way to send one-line mail out via command line using gmail?

Question

Using Raspbian and Ubunntu 16.04 LTS so need a generic Linux solution.

Requirement is simple:

I need a way to send one-line email messages from the command line.

I have set up a gmail account just for this particular Rpi3, with the address of rpi3abc@gmail.com - with no 2FA

So now I need to be able to send one-line mail messages from anywhere (including cron) without user intervention.

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I also would like it to be able to send text files; basically, anything from stdin.

Answer 1

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The simplest answer to sending one-line messages via gmail is to use ssmtp

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Install it with the following commands:

sudo apt-get update
sudo apt-get install ssmtp

Edit /etc/ssmtp/ssmtp.conf to look like this:

root=rpi3abc@gmail.com
mailhub=smtp.gmail.com:465
FromLineOverride=YES
AuthUser=rpi3abc@gmail.com
AuthPass=testing123
UseTLS=YES

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Send a one-liner like so:

echo "Testing...1...2...3" | ssmtp myusername@gmail.com

or

printf "Subject: Test\n\nTesting...1...2...3" | ssmtp myusername@gmail.com

Then, true to *nix, you just get the prompt back in a few seconds.

Check your myusername@gmail.com account, and voila, it is there!

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This also works well when sending a file, as so:

cat program.py | ssmtp myotherusername@yahoo.com

And the program will show up in the mailbox

If the file is a text file, it can have a first line that says Subject: xxxxxx

This can be used with various cron jobs can send me data with subject lines indicating the content.

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This will work with anything that prepares a message that is piped into ssmtp via stdin.

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For more details such as securing these files against other users and such, visit this article:

Send Email from Raspberry Pi Command Line

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Be sure to also look down below to the answer posted by Rui about locking down the FROM: address that might be changed in formatted message files, if necessary.

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Now if only I could figure out how to send SMS the same way.

Answer 2

ssmtp is just one of many Sendmail wrappers. All of these accept a message on standard input, and optionally a list of addresses as command-line arguments, and they all offer a binary named sendmail which implements (at least the basic features of) the traditional Sendmail command-line API. But properly speaking, that message needs to be well-formed RFC822 message. At minimum, it should have a Subject: header.

ssmtp address@example.com <<<$'Subject: testing 1...2...3'

(With ssmtp, sendmail is just a symlink to ssmtp. Postfix, Exim, and I believe every other MTA which Provides: mail-transport-agent has a similar arrangement, except of course sendmail where the sendmail binary is "the real thing".)

More commonly, you can piece together a simple email message with a here document.

/usr/lib/sendmail -oi -t <<____HERE
Subject: testing
To: recipient@example.net

Here we interpolate the shell variable $result
____HERE

(The Sendmail -t option says to take the recipient list from the headers of the message you receive on standard input. The precise path to Sendmail will differ between platforms.)

Another common variation is to combine the output of a few commands. Take care to have an empty line (a "neck") between the headers and the message body.

( printf "Subject: random number\n\n"
  dd if=/dev/urandom bs=4 count=1 2>/dev/null | od -D -An ) |
sendmail elsewhere@example.org

For anything beyond very simple ASCII text-only messages, you need to understand how to compose a proper MIME message, at which point it usually makes more sense to use a tool like mutt. Some platforms have a mail or mailx which knows how to send attachments and non-ASCII text, but this is not fully portable.

The challenge here is not finding a client which can take an email message and attempt to send it, it is to configure it for the specifics of Gmail, which requires the MTA to know the user name and password to use for the remote server in order to be able to use it as the outgoing smarthost.

Behind the scenes, most clients like mutt, mailx, etc typically just run sendmail behind the scenes to get the message off the system.

Answer 3

Adding to the OP own answer:

When configuring ssmtp, you may also forbid or allow users from defining the From, and also override the domain; you might want to do that for several reasons including the message not falling in the Spam folder.

You can add to /etc/ssmtp/ssmtp.conf:

# Where will the mail seem to come from?
rewriteDomain=my_internet_domain.uk

# Are users allowed to set their own From: address?
# YES - Allow the user to specify their own From: address
# NO - Use the system generated From: address
FromLineOverride=YES

Please note that while YES can be used in a home raspberry, it might not be advisable in a multi-user system from the security point of view.

Answer 4

I'm really partial to using mailx for this:

echo "Message body." | mailx -s "Subject line" -a /path/attachment.txt -r "Sender's Name<sender@email.com>" -c recipient2@email.com recipient1@email.com

Answer 5

What's wrong with "mail"?

echo "Hi there" | mail -s "Important mail" user@example.com

"mail" being /etc/alternative link to /usr/bin/bsd-mailx from bsd-mailx package. I believe it's there by default. Great utility for sending mail from cron scripts, for example.

Works on Ubuntu and FreeBSD as well.

Answer 6

I use sendEmail to send simple automated e-mails via an external provider's SMTP server:

sendEmail -q -f "me@mail.com" -u "mySubject" -t "someone@mail.org" -s "my.smtp.com" -o tls=yes -xu "mySmtpUser" -xp "mySmtpPw" -m "myMessage"

I pass everything on one line, so doing this on a command line would likely show all parameters (including smtp password) to all users, if they run a ps -ef while I am running the command. I use it within a shell script.

Answer 7

My server is CEntOS 7, and has sendmail but not mailx etc. Rather than install a new program I tested using sendmail directly, and found that this works:

echo -e "From: you@whatever\nTo: you@gmail.com\nSubject: this is the subject\n\nThis is the body,\nwith multiple lines." | sendmail -t

For me this seems to be the simplest way to send a short email, as it does not require running or configuring a server or daemon, and can be done in a single command line.

The idea is that a message will simply alert me that a certain program threw an error, without revealing any potentially confidential info, and then I'll SSH to the server to inspect its logs. This way there's no need to bother with complications like attaching files or encrypting the transport.

Notes:

• -e tells echo to interpret '\n' and other escapes.
• -t tells sendmail to get recipient addresses from 'To:' in the message header.
• If the mail does not arrive, use tail /var/log/maillogto see error messages.
• If sending to your gmail address, make a filter at gmail to keep them out of the junk folder.
• This sendmail is actually 'sendmail.postfix' (which might be normal); there's a man page here