How to select a high volume Mail Transfer Agent (MTA)

What is the best solution when choosing a high volume MTA? When selecting a Mail Transfer Agent (MTA), it is not just a technical question, it is important to see the differences and features to look for.

So, how does a sender select a high volume MTA for their emails? This important question I’ll answer in this article.

Technical and strategical factors influencing email deliverability

Deliverability is the ability to deliver emails to the recipient inbox, without hitting the spam or junk folder. Deliverability is affected by a combination of several factors both strategic and technical.

Strategic factors include for instance the type of content you are sending, list hygiene and sender reputation. Technical factors include sending limits, RFC and authentication compliance. Your email server provider or MTA platform should provide those to you to be compliant with the anti-spam and pass filters.

What problems does a high volume MTA solve?

Before focusing on how to select the right MTA and if you should go cloud or on-premises, let’s see the problems that a high performance MTA can solve.


Performance: a high-performance MTA is the best solution to send volumes of messages with high deliverability, high speed and low latency, while retaining full control of sending parameters. Besides, a dedicated MTA usually allows more detailed performance analysis via integrated reports and external analytic tools, and if well managed can lead to a higher level of reliability/availability.

Configurability: a high-performance MTA can usually be tuned all the way down to very specific configurations to separate and maximize the performance of different types of communication patterns for transactional emails, content emails (i.e. newsletters), promotional emails

You should be able to configure an MTA to behave the way that is most beneficial for your communication project, for example:

  • Use multiple sending queues, to segregate the email traffic and to prioritize your most important emails
  • Use multiple IP Pools, to ensure the timely sendings of the emails or to separate volumes with different reputations
  • Enable the authentication of the sender (DKIM signatures, Standard DMARC, SPF Configuration), to ensure your reputation identity
  • Configure throttling per domain, to comply with the provider imposed limits and optimize the number of messages delivered
  • Enable a detailed bounce classification and real-time management of errors and feedback loops, for timely analysis of sendings problem and comply with anti-spam rules

Choosing an MTA solution

If you are going to evaluate MTA options, selecting the right solution is very important. There are not a lot of different vendors that offer a commercial MTA. Here some advice I could give you:

  1. Be sure about performances and reliability of the vendor. Possibly ask for references from other clients or resellers. Be sure that the vendor has a good reputation and has been working in the industry for a long time. In summary, be sure that he knows what he is doing!
  2. Require price and technical transparency. An on-premises solution could be more convenient in the long term, but you need to be able to calculate the Total Cost of Ownership.
  3. Be sure that your vendor has a strong concern about privacy and data protection and is able to suggest you the best way to keep your data protected.
  4. Select a partner that can provide your company with ongoing supported consultancy both at the beginning and during the life of your project.
  5. Look at the features of the MTA software and select the solution that can assure you the best mix of options for your needs.
  6. Try to plan for the future: where do you see your project in the next few years? Find out beforehand the limits of your solution and the hidden cost of the migration between providers or between on-premises and cloud solutions.

These are the different type of features you want to be looking for:

  • outbound email authentication capability and monitoring (DKIM, DMARC, SPF);
  • outbound antispam/antivirus/RBL monitoring;
  • outbound connection/sending tuning (deliverability related features such as throttling, IP pools, connection pooling, connection limiting);
  • inbound bounce/feedback elaboration and routing capabilities;
  • multiple queue/priority sendings handling;
  • ease of use (web/software management, statistics, message search, log/data integration);
  • high-availabilty capabality (clustering);
  • reliability, authentication and accountability (storage type, clustering, error handling, logging);
  • installation format (software/virtual machine/appliance);
  • API/integration capabilities.

Cloud, on-premises and hybrid MTAs

Being an ESP and MTA vendor, we notice a growing demand of on-premises solutions in all industries. Very structured companies need to refer to a strong vendor able to play in both fields.

Some clients need to internalize their email sending infrastructure. Because of factors such as business models, email volumes or security and privacy policies and evaluate hybrid solutions (e.g.: In-house ESP and outsource MTA components).

Hybrid is an interesting scenario for those companies that want to satisfy their needs for privacy, full data control, and high deliverability performance. Email vendors should quickly adapt their proposition to offer flexible and sustainable solutions to satisfy the specific needs of clients from all industries. More about the differences in the modern considerations about Cloud versus on-premises in my next article.

About Fabio Masini

Fabio Masini is CTO of Diennea, one of the pioneering companies in digital direct marketing with two proprietary platforms: MagNews and EmailSuccess. After graduating in Computer Engineering, Fabio started his work in Diennea 14 years ago. First as Project Manager, after years of experiences with major clients, he deals now with the management of the entire technological infrastructure and company’s services.

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