SSMTP

Package ssmtp allow to have a minimalist smtp server to send email using a provider such as gmail

Important Note: ssmtp has been deprecated and is no longer maintained on debian-buster. source. The solution is to try msmtp.

Configuration

/etc/ssmtp/ssmtp.conf

# The user that gets all the mails (UID < 1000, usually the admin)
root=username@gmail.com

# The mail server (where the mail is sent to), both port 465 or 587 should be acceptable
# See also https://support.google.com/mail/answer/78799
mailhub=smtp.gmail.com:587

# The address where the mail appears to come from for user authentication.
rewriteDomain=gmail.com

# The full hostname.  Must be correctly formed, fully qualified domain name or GMail will reject connection.
hostname=yourlocalhost.yourlocaldomain.tld

# Use SSL/TLS before starting negotiation
UseTLS=Yes
UseSTARTTLS=Yes

# Username/Password
AuthUser=username
AuthPass=password
AuthMethod=LOGIN

# Email 'From header's can override the default domain?
FromLineOverride=yes

Send mail

with echo

echo -n 'Subject: test\n\nTesting ssmtp' | sendmail -v tousername@example.com

with file

mail.txt

To:username@example.com
From:youraccount@gmail.com
Subject: Test

This is a test mail.

sendmail -t < mail.txt