What device or application can provide throttling and load balancing rules in front of the MTA?
Summary
What email marketers say12Marketer opinions
Email marketer from Stack Overflow suggests using a load balancer like HAProxy in front of multiple Postfix instances. The load balancer distributes the load, and Postfix handles the actual mail delivery.
Marketer from Email Geeks explains that throttling should be done in the MTA to avoid only throttling the injection rate, but not the deliveries.
Marketer from Email Geeks suggests PMTA or GreenArrow as configurable MTA solutions. Later adding that hacking Postfix may be easiest if you have the in-house skill set. Commercial MTAs excel at performance, load balancing and have solid GUIs with vendor support. However, there is always a learning curve and systems integration issues.
Marketer from Email Geeks explains that the solution depends on your needs and skills, suggesting HAProxy with Postfix instances or commercial MTAs like GreenArrow Engine, PMTA, or MailerQ.
Email marketer from SparkPost shares their platform can manage sending reputation by providing insights to throttle and load balancing strategies. The platform provides tools to warm up IP's and domains as you scale email sends.
Email marketer from MXToolbox explains that while they don't directly offer a device, their monitoring tools can help identify performance bottlenecks in your MTA setup, enabling you to optimize throttling and load balancing strategies.
Email marketer from LinuxQuestions.org shares that using a combination of 'iproute2' for traffic shaping and multiple Postfix instances can provide a degree of load balancing and throttling. They emphasize the complexity and the need to understand the underlying networking.
Email marketer from StackExchange shares that using multiple public IP addresses and distributing email sending across them can help manage load and improve deliverability, especially when sending to different recipient domains.
Email marketer from Reddit mentions that using a message queue system like RabbitMQ or Kafka could help buffer emails before they hit the MTA. This provides a way to throttle email sending and prevent overwhelming the MTA.
Marketer from Email Geeks shares that they use Ongage for their front end, which has throttling capabilities and plugs into a number of ESPs.
Email marketer from Reddit suggests a Postfix setup with multiple outbound queues and different transport maps that route the mail differently based on the recipient domain. This helps throttle and load balance mail to different providers.
Email marketer from EmailOnAcid explains that load balancing can be achieved by distributing email sending across multiple MTAs or IP addresses, and emphasizes the importance of monitoring deliverability rates and adjusting sending strategies accordingly.
What the experts say2Expert opinions
Expert from Spamresource.com recommends controlling email volume with an application that sits in front of the MTA to ensure that you aren't sending too much mail. Spamresource.com also recommends managing reputation.
Expert from Word to the Wise explains that throttling should consider feedback loops and complaint rates, adjusting sending volume based on receiver responses to avoid deliverability issues. This implicitly addresses the load and throttling challenges.
What the documentation says5Technical articles
Documentation from HAProxy.org explains that HAProxy can be configured to load balance TCP traffic, making it suitable for distributing SMTP connections across multiple MTAs. It provides various load balancing algorithms and health checks.
Documentation from RabbitMQ explains that this message broker can act as a buffer in front of your MTA to smooth out traffic spikes, allowing you to throttle the rate at which messages are delivered to the MTA.
Documentation from Amazon AWS explains their Simple Queue Service (SQS) can be used to decouple the email sending process from the application, providing a buffer to manage and throttle email sending rates.
Documentation from Nginx.org shares that Nginx can be used as a TCP load balancer, distributing SMTP traffic to backend MTAs. It supports health checks and different load balancing methods.
Documentation from Postfix.org details that Postfix can be configured in a load-balanced setup with multiple instances behind a load balancer. It explains the configuration options required to ensure proper mail delivery.