Espresso is a permissions-based email client, that is designed to filter all unwanted mail from your Inbox by only allowing messages from known senders. All other emails are moved to a Junk folder for further review. The program integrates a challenge/response system that can automatically send and approval request to unknown senders, which allows them to verify their intend and be added to your list of approved senders. Messages can be approved based on the sender`s address, domain and also keyword in the subject or body of the message. If you have a limited range of people that you are in contact with, this type of spam control can be very effective, as it does not rely on filtering, but only allows the mail from the people or sites that you want to communicate with. You can always review the filtered messages to make sure you did not overlook any important message, and the program can automatically delete them after X days. Other features include message tagging, pre-configured support for Gmail and Hotmail, spell checking, integrated backup and more.Espresso supports POP3, IMAP4, HTTP protocols.