Difference between revisions of "SSMTP"

Latest revision as of 14:56, 9 September 2017

SSMTP is a program which delivers email from a local computer to a configured mailhost (mailhub). It is not a mail server (like feature-rich mail server sendmail) and does not receive mail, expand aliases or manage a queue. One of its primary uses is for forwarding automated email (like system alerts) off your machine and to an external email address.

ssmtp is unmaintained. Consider using something like msmtp instead.

Installation

Install the package ssmtp.

Forward to a Gmail mail server

To configure SSMTP, you will have to edit its configuration file (/etc/ssmtp/ssmtp.conf) and enter your account settings.

If your Gmail account is secured with two-factor authentication, you need to generate a unique App Password to use in ssmtp.conf. You can do so on your App Passwords page. Use the generated 16-character password in the AuthPass line. Spaces in the password can be omitted.

/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

Create aliases for local usernames (optional)

/etc/ssmtp/revaliases

root:username@gmail.com:smtp.gmail.com:587
mainuser:username@gmail.com:smtp.gmail.com:587

To test whether the Gmail server will properly forward your email:

$ echo test | mail -v -s "testing ssmtp setup" tousername@somedomain.com

Change the 'From' text by editing /etc/passwd to receive mail from 'root at myhost' instead of just 'root'.

# chfn -f 'root at myhost' root
# chfn -f 'mainuser at myhost' mainuser

Which changes /etc/passwd to:

$ grep myhostname /etc/passwd

root:x:0:0:root@myhostname,,,:/root:/bin/bash
mainuser:x:1000:1000:mainuser@myhostname,,,:/home/mainuser:/bin/bash

Security

Because your email password is stored as cleartext in /etc/ssmtp/ssmtp.conf, it is important to secure the file. Securing ssmtp.conf will ensure that:

• if any users have unprivileged access to your system, they cannot read the file and see your email password, while still letting them send out email
• if your user account is ever compromised, the hacker cannot read the ssmtp.conf file, and therefore your email password, unless he gains access to the root account as well

To secure ssmtp.conf, do this:

Create an ssmtp group:

# groupadd ssmtp

Set ssmtp.conf group owner to the new ssmtp group:

# chown :ssmtp /etc/ssmtp/ssmtp.conf

Set the group owner of the ssmtp binary to the new ssmtp group:

# chown :ssmtp /usr/bin/ssmtp

Make sure only root, and the ssmtp group can access ssmtp.conf:

# chmod 640 /etc/ssmtp/ssmtp.conf

Set the SGID bit on the ssmtp binary.

# chmod g+s /usr/bin/ssmtp

Finally add a pacman hook to always set the file permissions on /usr/bin/ssmtp after the package has been upgraded:

/root/bin/ssmtp-set-permissions

#!/bin/bash

chown :ssmtp /usr/bin/ssmtp
chmod g+s /usr/bin/ssmtp

Make the file executable:

# chmod u+x /root/bin/ssmtp-set-permissions

Now add the pacman hook:

/usr/share/libalpm/hooks/ssmtp-set-permissions.hook

[Trigger]
Operation = Install
Operation = Upgrade
Type = Package
Target = ssmtp

[Action]
Description = Set ssmtp permissions for security
When = PostTransaction
Exec = /root/bin/set-ssmtp-permissions

Now, all the regular users can still send email using the terminal, but none can read the ssmtp.conf file.

Sending email

To send email from the terminal, do:

$ echo "this is the body" | mail -s "Subject" username@somedomain.com

or interactively as:

$ mail username@somedomain.com

An alternate method for sending emails is to create a text file and send it with ssmtp or mail

test-mail.txt

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

This is a test mail.

Send the test-mail.txt file

$ mail username@somedomain.com < test-mail.txt

Attachments

If you need to be able to add attachments, install and configure Mutt and Msmtp and then go see the tip at nixcraft.

Alternatively, you can attach using uuencode:

$ uuencode file.txt file.txt | mail user@domain.com

References

• SSMTP and Gmail on the Arch forums
• Sending Email From Your System with sSMTP
• The Qnd Guide to ssmtp
• GMail Support - Configuring other mail clients