Phishing emails are one of the main attack vectors harming Internet users. We will build and experiment with a prototype system, our custom-built version of the Tuta Mail webmail service, to defend against these threats. The system would be an addition to the web-based email service, that will add support for the defense against phishing emails. The main defense mechanisms include authentication of messages from trusted senders (using digital signatures), ability to send signed messages, and a user-interface mechanism to train users to detect (phishing) messages that appear as if they were sent by one of the senders trusted by the user.