Understanding IP based rate limiting and throttling in PowerMTA


PowerMTA is an intelligent infrastructure for customer email management. However, the IP based rate limiting and throttling are the most misunderstood and misconfigured features in email management system.

The rate-limiting refers to the number of requests a user can make in a given period of time. Rate limiting is used for security purposes. It can slow the brute force password guessing attacks by limiting the incoming requests to a set limit (for real users).

Rate limiting also protects the upstream application servers from overloading due to too many user requests at the same time. Let’s look the IP based rate limiting in PowerMTA.


What is IP based rate limiting in PowerMTA?

One of the new features introduced in PowerMTA is IP based rate limiting. For those who don’t know rate limiting algorithm is used to control the rate of traffic sent or received by a network interface controller. It plays an important role in preventing DDoS attacks.

In PowerMTA, the IP based rate limiting uses “source-ip-max-msg-rate” directive which is available per domain. Thanks to the new feature, admins and delivery engineers now will have more control over the email management system.

The IP based rate limiting allows the engineers to specify the maximum number of recipients on per-second, per-minute, and the per-hour basis for each domain and each IP address.

The new feature is used by senders to define multiple IPs in single VirtualMTA. VirtualMTA is an email technology and part of PowerMTA email delivery system that allows senders to control the source IP address for each email message.

In PowerMTA application, the VirtualMTA manages the delivery functions independently. It is primarily known to have higher and precise mailing delivery control with options to enable or disable DomainKeys. With the new IP based rate limiting, the sender can limit the attempted delivery rate for each IP address in VirtualMTA to the respective domains. This increases the chances of the mail being successfully delivered to the inbox, unless the IP is blacklisted.

The throttling in PowerMTA can also be achieved through the “source-ip-max-connect-rate” directive. It allows control over the maximum number of connections that can be attempted per IP address and per domain or Virtual MTA at specified time interval.


How is IP Monitoring service used for throttling in PowerMTA?

The IP based monitoring service is also useful in throttling in PowerMTA. If the IP based monitoring service sends an alert to the server regarding excessive bounces or complaints, the PowerMTA email management server springs into action by quickly throttling at the source IP and preserving the reputation of your domain.

The IP reputation is an important element in email delivery system which is determined by the Smart Network Data Service (SNDS) and Sender Score. Many email service providers have a list of blacklisted IPs which is determined by low SNDS and Sender Score.

PowerMTA has an intelligent feature where the sender receives an email notification if any of the metrics (SNDS and Sender Score) decreases below a threshold level.

The notifications are sent on the as-need basis that helps you prevent IP reputation issue. The throttling and IP based rate limiting work in hand in hand to improve and maintain high-score in email deliverability and protect your IP reputation.

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