How do I use sendmail on Debian/Ubuntu to send emails without SMTP or other modules? I have a Drupal 8 installation and it's not sending emails. I've configured postfix and tested using sendmail command line. PHPMailer module is installed via composer. When I submit passowrd reset request, error message is "Unable to send email. Contact the site administrator if the problem persists."

I checked the /var/log/mail.log file and the following error is shown: "Recipient addresses must be specified on the command line or via the -t option"

How can I use sendmail with Drupal 8? This seems like it "should" be easy, but all documentation I've found says install an SMTP module.

Thanks for any clues / advice.
OK, thanks to Clive I stopped assuming things and checked the php.ini file. Sure enough the sendmail_path option just had "/usr/sbin/sendmail".

I've updated php.ini with "sendmail_path = /usr/sbin/sendmail -t -i" and it's working beautifully.

Doh!