New Feature in PowerMTA v4.5: IP Based Rate Limiting

By Port25

One of the noteworthy features in PowerMTA's new v4.5 release is IP based Rate Limiting. The feature, enabled via the new per domain "source-ip-max-msg-rate" directive, is designed to give delivery engineers/admins additional control. IP based rate-limiting allows for throttling the number of attempted recipients on a per-hour, per-minute and per-second basis separately for each IP address for each domain/VirtualMTA. This feature will be primarily used by senders that define multiple IPs in a single VirtualMTA and that want to limit the attempted delivery rate for each IP address in the VirtualMTA to the respective domains.

In addition, IP connection rate limits can now also be controlled via the "source-ip-max-connect-rate" directive, which allows one to specify the maximum number of connections to be attempted during the specified time period per IP per domain/vmta.

Backoff Insight

In previous versions of PowerMTA the only method to know why a queue entered backoff mode was to check the log file or to setup the backoff-notify directive. Now PowerMTA will show the "error" that caused the queue to go into backoff mode in the individual queues of the web monitor as well as in these commands:

pmta show queues domain/vmta
pmta show topqueues domain/vmta

IP based rate-limiting and Backoff Insight, are just two features of the latest release of PowerMTA v4.5, which is available now for download.

IP Monitoring Service

If you receive an alert from your IP based monitoring service, such as excessive bounces or complaints, one of the most critical elements to preserving your IP reputation is the ability to quickly throttle at the source IP. The best tool I've seen has recently just launched by Postmastery. They offer IP reputation monitoring based off of SNDS Status and Sender Score. They also cross-reference your IP to a database of blacklists. You'll receive real-time notifications via email based off of any decreases in any of the metrics above. Notifications are sent on an "as needed" basis- you're notified at the beginning of a potentially forming IP reputation issue. So, if there's any decrease in IP reputation or a high number of complaints, you'll know about it very quickly. There's also a weekly email with a summary of all IPs being monitored and their current rep/status. Postmastery also has the ability to use SNDS API keys to aggregate data from that as well, showing complaints from SNDS domains. Contact Maarten Oelering at

Related topics: Email