====== SSMTP ======

See also **[[networking:linux:postfix_smarthost|Postfix Authenticated Smarthost]]** (Does the same thing without requiring the EPEL repo.)

http://www.linux.com/archive/feature/132006

http://www.squad17.org/node/39

SSMTP is a simple replacement for a full MTA such as Sendmail or Postfix.

  * if you already have Postfix installed (RHEL/CentOS), see the link above
  * no server daemons
  * no running processes
  * lightweight
  * flexible
  * easier than dealing with an MTA
  * be sure all you need is a simple outbound sendmail command replacement

===== Installation =====

==== Ubuntu ====

<file>
apt install ssmtp bsd-mailx
</file>

==== CentOS ====

See also **[[computing:linux:epel|Using the EPEL Repository]]**

Install ssmtp:

<file>
yum install ssmtp --enablerepo=epel
</file>

On one older system, ''mdadm'' depended on ''sendmail'', I had to do this first:

<file>
rpm -e --nodeps sendmail
</file>

===== From Address =====

<note important>In modern times, secure mail servers are very strict about who is authorized to send mail.  You generally must use a **valid sender e-mail 'from address'** that **matches the authentication credentials** used.</note>

<note>Using ''FromLineOverride=YES'' will allow the sender to specify the 'from address' at the time of sending.  ''FromLineOverride=NO'' will force the 'from address' to the ''root=validsender@domain.tld'' line in ''ssmtp.conf''.</note> 

For sending **system or 'root' mail**, you will probably have to manipulate the 'from address' to get SSMTP to send mail through a secure mail server.

<file>
vi /etc/ssmtp/revaliases

root:validsender@domain.tld
</file>

===== Configuration =====

For **SSL** connections on **SMTPS port 465**:

<file>
vi /etc/ssmtp/ssmtp.conf

root=validsender@domain.tld      # will be the 'from address'
mailhub=mail.domain.tld:465      # to use SSL on port 465
RewriteDomain=domain.tld         # instead of the host name
#hostname=_HOSTNAME_
#FromLineOverride=YES            # allows setting 'from address' at runtime
UseTLS=YES                       # for SSL
AuthUser=smtpuser
AuthPass=smtppass
#Debug=YES                       # useful for troubleshooting
</file>

:!: If you want to use **TLS** connections on **Submission port 587**, you will need to add/change:

<file>
mailhub=mail.domain.tld:587
#UseTLS=YES
UseSTARTTLS=YES
#TLS_CA_File=/etc/pki/tls/certs/ca-bundle.crt   # Depends on configuration - Not needed on Ubuntu 18.04
</file>

:!: If you don't specify a ''hostname'', SSMTP will query the local machine.  Since we are authenticating, the hostname doesn't matter too much.

===== Test =====

:!: If desired, enable (un-comment) the **debug** line, then look in ''/var/log/maillog''.

If desired, install the ''mail'' command:

<file>
yum install mailx

update-alternatives --config mta
</file>

==== Send a Test Message ====

<file>
echo test | mail -s "testing ssmtp" tester@yourdomain.com
</file>

Or with no ''mail'' command and no subject line:

<file>
echo test | ssmtp -v -f "from@domain.tld" -F "Full Name" tester@yourdomain.com
</file>

or

<file>
echo test | sendmail -v tester@yourdomain.com

tail -f /var/log/mailog
</file>

==== Another Test ====

<file>
cat << EOF >> /tmp/test.eml
From: Full Name <validsender@domain.tld>
To: Test User <tester@somedomain.tld>
Subject: For test only!


EOF

ssmtp -t < /tmp/test.eml
</file>

===== Troubleshooting =====

<file>
Debug=YES
</file>

<file>
tail -30 /var/log/mail.log
</file>

===== Change the Default MTA =====

On Centos:

<file>
alternatives --config mta
</file>