mail: unrecognized option '-S' | sending mail from linux server

Question

I am trying to run a bash to send emails from my linux server. I am using the following command:

echo "This is the message body" | mail -s "This is the subject line" -a "From: <Sender>" -a "To: <recipient>" -S smtp="smtp.gmail.com:587" -S smtp-use-starttls -S ssl-verify=ignore -S smtp-auth=login -S smtp-auth-user=$SMTP_USER -S smtp-auth-password=$SMTP_PASS <recipient_email_address>

I am receiving the error: mail: unrecognized option '-S'

As far as I read, previously mailx was used but this error shouldn't occur with mail command. can you please help me where I am going wrong?

System Info: Ubuntu 20.04.5 LTS (GNU/Linux 5.15.0-1040-azure x86_64)

mail --version >> mail (GNU Mailutils) 3.7

Answer 1

The -S option to set a variable is recognised (only) by Heirloom mailx. You've got mail from GNU mailutils, which does not support this option.

If you need to set your SMTP values on the command line you will need to install Heirloom mailx. Otherwise look at getting your MTA (Mail Transport Agent) configured properly to do this all for you. For this simple case of forwarding, I would suggest you consider msmtp (configuration suggestions on the ArchWiki, which include a recipe for sending through Gmail).