Exim

The sendmail Sentrion platform is specifically designed for large, complex environments, but we make a subset of that solution available as an open-source offering. Sentrion is not for everyone, but if you are using open source email for a large complex environment and need an enterprise platform that will enable your messaging roadmap for years to come (virtualization, consolidation, cloud migration, etc.). The Domain Keys Identified Mail (DKIM) Internet standard enables email senders to digitally sign their messages so that receivers can verify that those messages have not been forged. The DKIM sender authentication scheme allows the recipient of a message to confirm a message originated with the sender’s domain and that the message content has not been altered. A cryptography-based solution, DKIM provides businesses an industry-standard method for mitigating email fraud and protecting an organization’s brand and reputation at a relatively low implementation cost.

MailerQ is a high-performance on-premise Mail Transfer Agent (MTA) for delivering millions of emails per day. It is built with a strong focus on performance, ease-of-use, and insights. The MTA comes packed with an intuitive Management Console, REST API, and other functionality necessary for every serious sender to retain and improve their sender reputation and deliverability rates. That’s why it's increasingly becoming the preferred solution of choice for senders of all kinds, from Email Service Providers and e-commerce platforms to banks and government institutes. The management console allows for real-time insights in delivery attempts and results, queues, error logs and a lot more per MTA, IP, target and even per customer, campaign or message type. Response patterns allow you to classify bounces, process feedback loops and adapt MTA behavior based on server responses. This will help you maximize your email deliverability and sender reputation.