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GNU/Linux - sendmail to send emails from CLI or scripts

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I will put here some tricks that I use to send emails with the sendmail command.

sendmail command is very usefull to send emails in bash scripts.

Install and Configure SSMTP

I personnaly use a private mail server but but it should also work with a gmail account.

Note: To do so, you need to enable less secure app (https://support.google.com/) in your gmail settings.

I don't use Exim anymore because it's horrible to set up under Debian.

  • Install ssmtp:
root@host:~# apt update && apt install ssmtp
  • Edit /etc/ssmtp/ssmtp.conf:
# # Config file for sSMTP sendmail # # The person who gets all mail for userids < 1000 # Make this empty to disable rewriting. #root=postmaster # The place where the mail goes. The actual machine name is required no # MX records are consulted. Commonly mailhosts are named mail.domain.com mailhub=std.rocks:465 # Where will the mail seem to come from? rewriteDomain=std.rocks # The full hostname hostname=server.std.rocks # 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 root=rapport@std.rocks TLS_CA_FILE=/etc/ssl/certs/ca-certificates.crt UseTLS=Yes UseSTARTTLS=No # users which is allowed to send mail AuthUser=john@std.rocks AuthPass=MyP@ssW0rd AuthMethod=LOGIN

Sending emails

Simple

  • Create a /tmp/mail.header file and write header :
To: user@shebangthedolphins.net From: john@std.rocks Subject: test mail Hello human world! This message has been sent with sendmail!
  • Send the mail :
user@host:~$ cat /tmp/mail.header | sendmail -f john@std.rocks user@shebangthedolphins.net

Send mails from a file list

  • Create /tmp/mail.list file :
user01@shebangthedolphins.net user02@shebangthedolphins.net user03@shebangthedolphins.net
  • Create a /tmp/mail.header.origin file with a temp@address wich will be replaced later :
To: temp@address From: john@std.rocks Date: Thu, 17 Jun 2021 08:45:25 +0200 Subject: test mail
  • Create a /tmp/body :
Hi, this message has been sent with sendmail!
  • Send emails :
user@host:~$ for i in $(cat /tmp/mail.list | sort -R | head -n 1); do sleep 20; cp /tmp/mail.header.origin /tmp/mail.header; echo "sending mail to $i"; sed -i "s/temp@address/$i/" /tmp/mail.header; sed -i "s/Date:.*/Date: $(date -R)/" mail.header; cat /tmp/mail.header /tmp/body | /usr/sbin/sendmail -f john@std.rocks "$i"; done
  • Same but easier to read :
for i in $(cat /tmp/mail.list | sort -R | head -n 1); do sleep 20s #wait 20 second beetween each mail cp /tmp/mail.header.origin /tmp/mail.header #copy template header to current header echo "sending mail to $i" #echo current recipient sed -i "s/temp@address/$i/" /tmp/mail.header #replace temp@address by current recipient mail address in /tmp/mail.header sed -i "s/Date:.*/Date: $(date -R)/" /tmp/mail.header #replace Date field by current date in /tmp/mail.header cat /tmp/mail.header /tmp/body | /usr/sbin/sendmail -f john@std.rocks "$i" #send email to current recipient done

Send mails from a file list

user@host:~$ for i in $(seq 1 60); do sleep 4h; for i in $(cat /tmp/mail.list.txt | sort -R | head -n 1); do cp /tmp/mail.header.origin /tmp/mail.header; echo "sending mail to $i"; sed -i "s/temp@shebangthedolphins.net/$i/" /tmp/mail.header; grep Date mail.header | sed -i "s/Date:.*/Date: $(date -R)/" mail.header; cat /tmp/mail.header /tmp/body | /usr/sbin/sendmail -f user@shebangthedolphins.net "$i"; done; done /tmp/mail.header X-Priority: 1 (Highest) From: sender@shebangthedolphins.net To: temp@shebangthedolphins.net Date: Thu, 17 Jun 2021 08:45:25 +0200 Subject: STD : Subject that I want Content-type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit IME-Version: 1.0 Disposition-Notification-To: <sender@shebangthedolphins.net> cat /tmp/body Hello human world!

Headers tricks

If needed, we can add some headers :

  • Define content type and charset :
Content-type: text/plain; charset=utf-8
  • Set Mime-Version (Normally automatically added):
Mime-Version: 1.0
  • Set highest priority:
X-Priority: 1 (Highest)
  • Enable notification, to notify the sender about the ultimate disposition of the message :
Disposition-Notification-To: <sender@shebangthedolphins.net>

Send an email with an attachment

  • Convert the file to be sent to base64:
user@host:~$ base64 secret.svg PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSI5MDAiIGhlaWdo dD0iNjAwIj48cGF0aCBmaWxsPSIjRUQyOTM5IiBkPSJNMCAwaDkwMHY2MDBIMHoiLz48cGF0aCBm aWxsPSIjZmZmIiBkPSJNMCAwaDYwMHY2MDBIMHoiLz48cGF0aCBmaWxsPSIjMDAyMzk1IiBkPSJN CAwaDMwMHY2MDBIMHoiLz48L3N2Zz4=
  • Edit /tmp/body:
--19032019ABCDE Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Hi, this message has been sent with sendmail! --19032019ABCDE Content-Type: application/svg; name="secret.svg" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="secret.svg" PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSI5MDAiIGhlaWdo dD0iNjAwIj48cGF0aCBmaWxsPSIjRUQyOTM5IiBkPSJNMCAwaDkwMHY2MDBIMHoiLz48cGF0aCBm aWxsPSIjZmZmIiBkPSJNMCAwaDYwMHY2MDBIMHoiLz48cGF0aCBmaWxsPSIjMDAyMzk1IiBkPSJN CAwaDMwMHY2MDBIMHoiLz48L3N2Zz4= --19032019ABCDE
  • Edit /tmp/header:
To: user@shebangthedolphins.net From: john@std.rocks Date: Thu, 17 Jun 2021 08:45:25 +0200 Subject: test mail Content-type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit IME-Version: 1.0 Content-Type: multipart/mixed; boundary="19032019ABCDE"
  • Send email:
user@host:~$ cat /tmp/mail /tmp/mail | sendmail -f john@std.rocks user@shebangthedolphins.net