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An Open Source Perspective on Commercial MTAs

Email Infrastructure: Open Source vs. Commercial MTAs – Port25 white paper addressing a number of frequently asked questions on the core differences between open source Mail Transfer Agents (MTAs) and commercial MTAs. (Learn More)It’s always refreshing to obtain a different perspective, especially from the open-source community regarding email sending infrastructure. For those who are currently utilizing an open-source product, we thought this feedback from one of our constituents would be valuable for decision makers.

From feedback regarding our Open Source vs. Commercial MTA white paper, an advocate of open source sending software, Matt Sergeant, provided his own viewpoints between the tangible differences of open source and commercial MTA software. Based on these perspectives we updated the white paper to give readers and decision makers a more objective thread on why commercial MTAs are such a critical investment for enterprise level sending environments. Below is Matt’s perspective:

Things commercial MTAs offer that (most) open source MTAs don’t:

  • Cluster support
  • Monitoring (including cluster monitoring)
  • Sophisticated Bounce Management
  • Per recipient domain settings
  • VirtualMTA Technology
  • Email Encryption
  • Scheduled Delivery Control
  • IP Based Rate Limiting
  • 30+ Custom Retry Intervals
  • Real Time Bounce Diagnostics
  • Back off reason insight

Cluster Support

Commercial MTAs usually have some form of built-in support for centralized management of a cluster of servers. This can be as basic as shared configuration data, or as complex as full control of every machine in the cluster from a centralized management console, shared information between instances of current connection counts to recipient domains, and cluster-wide monitoring. This is only one benefit for the new PowerMTA Management Console introduced this past year by Port25.


Most commercial MTAs have built-in monitoring support. To monitor open source MTAs you often need to install some external monitoring tool (such as Nagios) and rely on whatever support is built into that tool for monitoring your mail server. Alternatively you end up writing your own monitoring software, or plugins for your monitoring software of choice. This becomes particularly tricky when you have multiple servers, and need to be able to monitor as both an aggregate and be able to “drill-down” into individual servers.

Sophisticated Bounce Management

Modern commercial MTAs have sophisticated algorithms that they have built up over years of experience for managing bounces. Because the SMTP RFCs are often unclear on giving reasons why a mail may have bounced, these commercial MTAs have built up techniques for understanding responses from different types of recipient MTAs, providing the administrator of the commercial MTA with the appropriate tools for dealing with bounces in a manner which is appropriate given the information at hand.

Per Recipient Domain Settings

While some open source MTAs have some level of per-domain settings for outbound email, this is often rather complex to code or doesn’t exist at all. Commercial MTAs were mostly borne from the need for large senders, and so having flexible configuration on a per-recipient domain basis is a basic requirement.

TLS over SMTP Reporting

The use of the Transport Layer Security (TLS) protocol over SMTP offers certificate-based authentication and helps provide security-enhanced data transfers by using encryption keys. With the sending industry moving to a more secure and encrypted sending model, it is necessary to “track” if a given message was delivered over a secure socket and if so, what protocol and cipher were used.

Commercial MTAs now have the ability to encrypt outbound email with TLS over SMTP. Both the receiver and the sender must have email encryption enabled. As we move towards email encryption as a standard Port25 has optimized performance in it’s latest version v4.5. For example, commercial MTAs now have granular reporting on TLS over SMTP. You now have the ability to know if a message was sent over an encrypted connection. The benefit is important if your client, for example, is a financial institution and requires proof of security.

By Port25, A Message Systems Company

Port25, A Message Systems Company, provides highly focused email delivery software that addresses the ever-expanding needs of client communications and digital messaging apps. Port25’s flagship product, PowerMTA™, has a global footprint, with over 4,000 installations in more than 51 countries.

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