The most powerful MTA

MailerQ is a high performance MTA, designed to handle large volumes of email.


MailerQ is fast. It runs multiple parallel threads to deliver email, network calls are non-blocking and messages never hit a disk.


MailerQ uses message queues and JSON, giving you full control over your email flow. You can monitor and intervene when necessary. Prioriziting and routing has never been easier.


MailerQ is competitive. It beats every MTA in performance and pricing, and it has all the features that you find in other MTA's.

Architecture and flexibility

For most MTA's, disk performance is the bottleneck. But not for MailerQ. MailerQ is an MTA and handles incoming and outgoing SMTP traffic and processes MIME data. But it does not write to disk. It relies on RabbitMQ and NoSQL storage for messages queues and deferred messages. These tools are fast, reliable and scalable and were designed to handle big data flows, and do that much better than an MTA could ever do.

All data that passes through MailerQ is JSON encoded. The messages that you inject and the incoming messages are all consumed from and published to RabbitMQ as JSON objects. The delivery results are also JSON encoded and hold properties like the SMTP status code, the certificate details of the receiving server and much more.


RabbitMQ is a tool for message queueing. You can create your own mail flow that passes through filters and scripts, or that can be forked and sent to mailboxes, monitors or logs.


MailerQ connects to a MongoDB or Couchbase server to store deferred messages. If you do not want to use one of these tools, you can configure MailerQ to use disk based storage instead.

Hardware requirements

MailerQ runs in multiple threads to use all your CPU's. Each of these threads has a non-blocking architecture: MailerQ does not wait for slow system calls or blocking network operations. Messages do not get stored to disk, because disk operations slow down software too. This all makes that you can send millions of messages from a single server.

The table holds the hardware requirements if you would run MailerQ, RabbitMQ and MongoDB all on the same physical machine, using gzip compression for data interchange. For a high availability setup (to survive hardware failures) it is better to setup a cluster of two or three machines.

Emails/day Servers Specs
1 million 1 2vCPU, 6GB RAM, 100GB HDD, 100Mbps
10 million 1 6vCPU, 10GB RAM, 300GB HDD, 1Gbps
50 million 1 24vCPU, 60GB RAM, 1400GB HDD, 256GB SSD, 1Gbps
100 million 1 48vCPU, 120GB RAM, 3250GB HDD, 512GB SSD, 2Gbps

Simple configuration

Other MTA's get their settings from long and complex configuration files that are hard to maintain and difficult to update. However, you want your MTA to be easy to tune, both manually and programmatically. This is possible with MailerQ.

Most of MailerQ's runtime configuration settings come from a relational database. This allows you to update on the fly: connect to the database and run queries to insert or update data. MailerQ picks up the new settings automatically. No restart or reload is needed. This is perfect if you want to integrate MailerQ into other dashboards, API's or scripts.

Supported database engines

MailerQ supports a couple of database engines: MySQL, PostgreSQL and Sqlite. You can use the one that fits you best. The databases are only used for configuration settings, not for realtime queries. MailerQ periodically copies all settings to main memory to speed up the lookups. The database therefore never is the application's bottleneck, and slow queries never slow down delivery.

Management console

MailerQ comes with a web-based management console, where you adjust deliverability settings on the go. You can use this dashboard if you do not want to connect to the database. The management console also allows you to monitor the real-time performance of your deliveries and IP's, reroute emails to other IP addresses or set up flood patterns to react to server responses.

Real-Time statistics Per domain performance SMTP monitoring


MailerQ comes packed with features right out of the box to improve your email deliverability.


Validation mechanisms

  • SPF
  • DKIM
  • ARC
  • SpamAssassin
Injection mechanisms

Injection mechanisms

  • JSON over AMQP
  • Spool directory
  • Command Line Interface
  • SMTP
Supported extensions

Supported SMTP extensions

  • DSN
Delivery parameters

Delivery parameters

  • Domain, MTA and IP based rates
  • Support for per-message overrides
  • SMTP reply pattern matching
  • Configurable deferral periods
  • And much, much more...
Management console

Management console

  • Realtime overview
  • Live SMTP traffic monitor
  • Live logfile monitor
  • Delivery settings
  • Automatic recognition of domain groups
  • Pause and resume campaigns based on message tags
  • And more...

MIME handling

  • Header insertion/modification
  • Personalisation
  • CSS stylesheets to attributes
  • JSON to MIME conversion
  • DKIM and ARC message signing
Incoming messages

Incoming messages

  • DMARC report handling
  • DSN handling
  • Local address database

Advanced settings

  • Support for clustering and chaining
  • Smarthost support
  • C/C++ plugin API


The license tariff is, besides a small fixed price, based on the number of IP addresses that you use to send out email from.
We offer yearly and monthly licenses. You can use the same license for multiple servers.

  Price/month Price/year
License fee
€ 125 / month
€ 1250 / per year
First 5 IPs
Next 10 IPs
All next IPs
€ 10 / IP per month
€ 1 / IP per month
€ 100 / IP per year
€ 10 / IP per year

What is an MTA?

An MTA is an application that runs on your own servers to send and receive email. MTA's are used by ISP's and ESP's and large organizations that handle their own mail.

Prefer a cloud-based solution?

Would you rather not get your hands dirty with installing, configuring and hosting MailerQ yourself? SMTPeter might be something for you. SMTPeter is a cloud-based SMTP server for fast and secure email delivery, based on MailerQ.

Learn more about SMTPeter