sSMTP is a send-only sendmail emulator for Linux. It replaces sendmail, in place, but implements only send features.

Install and configure sSMTP

On QTS 5.X, sSMTP is already installed.

However, it is not the standard ssmtp binary:

  1. it doesn't support providing recipient as argument (ie. the standard sendmail Recipients must be provided as header in the message:
    Subject: This is a subject
    Did you receive this message?
  2. the configuration file is not in standard location (/etc/ssmtp/ssmtp.conf): /etc/config/ssmtp/ssmtp.conf

Configure sSMTP on TS-243E

Use the UI and QNAP's Notification center interface, add an email.

clicks in QTS UI to create email account

QNAP's QTS configures authentication with Gmail through Oauth token-based authentication.

This can't be achieved (to my knowledge) in command line, but this is more secure than an Application Password stored in plain text (see Configure sSMTP with Gmail on Ubuntu).