When you first log in, you will create an "email forwarder" with a unique keyword on the "kopi.cloud" domain. Any time someone sends mail to that forwarder, Kopi will forward that mail to your real inbox. This way, the sender of the mail never knows your real email address.
You can even reply to forwarded mail and Kopi will forward your reply email to the original sender - all the while keeping track of the addresses involved and never revealing your real email address to the original sender.
Trial users are limited to one forwarder on the "kopi.cloud" domain and replies for trial users may be queued behind paying subscribers' mail, which may cause a delay.
If someone is abusing the address you gave them, you can block that address from delivering mail to your real email inbox with a single click in the Kopi app.
All blocked mail is visible within the Kopi for at least a month. You can tell Kopi to override and send a single blocked email to your real inbox with a single click.
You can also decide to publish blocked mail for a forwarder to an RSS feed. You can then subscribe your RSS reader to that feed and browse blocked emails at your leisure.
RSS redirection is very handy for dealing with sites like StackOverflow or LinkedIn, where you don't want to see most of the mail in your inbox but might want to review the blocked mail.