MassMailer - MassMailer lets users send mass emails from within Salesforce.
HEY - Email at its best, new from Basecamp.
InstAddr - Disposable email address application.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
Greatmail - Greatmail is an email hosting service provider built for businesses of all sizes.