Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.
InstAddr - Disposable email address application.
HEY - Email at its best, new from Basecamp.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Soverin - Soverin is the honest email service that doesn’t sell your data.
Mail.be - Mail.be Virtual office