SendinBlue is a SaaS solution for relationship marketing.

FastMail is an email service offering paid email accounts for individuals and organizations.

SquirrelMail provides both a web-based email client and a proxy server for the IMAP protocol.

hMailServer is a free open source email server for Microsoft Windows.

OpenMailBox is a free mail hosting service.

Pepipost provides a cloud based transactional email delivery infrastructure which is reliable, scalable, secure and easy-to-use.

Mailgun is the email automation engine for sending, receiving and tracking emails.

SendGrid is a customer communication platform for transactional and marketing email.