Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Brevo - Innovative online Email Marketing solution to manage your contacts, create & send your newsletters and track your results. More than 80 000 clients. Best prices and attractive features.
Roundcube - Web-based IMAP email client
Litmus - litmus tests and tracks your email campaigns, so you can always put your best design forward.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.
Return Path - Inbox placement solutions from Return Path helps improve email deliverability and increases email marketing ROI.