sSMTP

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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.

Note: sSMTP is unmaintained. Consider using something like msmtp or OpenSMTPD instead.

Installation

Install the package ssmtp^AUR.

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 you Gmail username (not the App Name) in the AuthUser line and use the generated 16-character password in the AuthPass line, spaces in the password can be omitted.
If you do not use two-factor authentication, you need to allow access to unsecure apps. You can do so on your Less Secure Apps page.

/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
TLS_CA_FILE=/etc/ssl/certs/ca-certificates.crt
UseTLS=Yes
UseSTARTTLS=Yes

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

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

Note: Take note, that the shown configuration is an example for Gmail, You may have to use other settings. If it is not working as expected read the man page ssmtp(8), please.

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 -e 'Subject: test\n\nTesting ssmtp' | sendmail -v tousername@example.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 myhost /etc/passwd

root:x:0:0:root at myhost,,,:/root:/bin/bash
mainuser:x:1000:1000:mainuser at myhost,,,:/home/mainuser:/bin/bash

Security

Because your email password is stored as cleartext in /etc/ssmtp/ssmtp.conf, it is important that this file is secure. By default, the entire /etc/ssmtp directory is accessible only by root and the mail group. The /usr/bin/ssmtp binary runs as the mail group and can read this file. There is no reason to add yourself or other users to the mail group.

Sending email

To send email from the terminal, do:

$ echo -e "Subject: this is the subject\n\nthis is the body" | mail user@example.com

or interactively as:

$ sendmail username@example.com
Subject: this is my subject
CC: optional@example.com

Now I can type the body here

Note: When using mail interactively, after typing the Subject: subject and other headers, hit enter twice, and then type the body. Hit Ctrl+d on a blank line to end your message and automatically send it out.

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

test-mail.txt

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

This is a test mail.

Send the test-mail.txt file

$ sendmail -t < test-mail.txt

Some users might prefer the syntax of mail from s-nail, mailutils, or other mailx providers instead. For example, mail has options to provide the subject as an argument. mail requires sendmail and can use ssmtp^AUR as sendmail.

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 from sharutils. To attach 'file.txt' as 'myfile.txt':

$ uuencode file.txt myfile.txt | sendmail user@example.com

Mail to Local Users

Messages sent to local users (or any other address not ending in @fqdn are treated in one of two ways

destination user has UID < 1000 - The address is replaced by the address defined by root=user@fqdn in /etc/ssmtp/ssmtp.conf
destination user has UID ≥ 1000 or the user is unknown - The the value from rewriteDomain= in /etc/ssmtp/ssmtp.conf is appended to the end of the user id.

This can lead to problems if local users on your system are not also valid users at your rewriteDomain, but are receiving mail from system services, esp if your rewrite domain is a public service like gmail.com.

To work around this, you can use mail from s-nail. The mail command can read aliases defined in /etc/mail.rc. Example:

$ grep alias /etc/mail.rc

alias git git<username@example.com>
alias archuser 'My Name'<someone@example.com>

You can then pipe messages into mail instead of into sendmail.

$ echo -e "Hey archuser." | mail archuser

Note: You might be tempted to symlink sendmail to /bin/mail. Do not do this. sendmail and mail have different syntax for both arguments and standard input. It is better to find the processes that are using sendmail directly and configure them to use mail instead.