In PowerMTA (PMTA), a "hot" configuration generally refers to high-volume or "aggressive" delivery settings, often used for warming up IPs or sending to high-reputation recipients. This configuration is typically managed within the /etc/pmta/config Sample High-Volume (Hot) Config Review A robust PowerMTA configuration uses
directives to control delivery traffic. Below is a review of standard "hot" parameters: Moving from PowerMTA - KumoMTA
Here’s a solid, in-depth review of what a “sample PowerMTA configuration file” should look like — especially if you’re searching for a “hot” (high-performance, deliverability-focused) setup.
I’ll break down the key sections, explain what each does, and highlight what makes a config hot versus just functional.
<domain hotmail.com> max-smtp-out 10 max-msg-rate 20/s use-rs yes use-plaintext yes smtp-pipelining yes smtp-starttls required </domain>
<domain gmail.com> max-smtp-out 15 max-msg-rate 30/s use-rs yes smtp-starttls required </domain>
<domain yahoo.com> max-smtp-out 8 max-msg-rate 15/s smtp-starttls required </domain>
log-file-rotate daily
smtp-listener 0.0.0.0:25 default-virtual-mta vmta-pool-1 authenticate plain login source smtp-source-inject
The config includes dkim-sign yes. A "hot" config handles authentication internally. Instead of signing the mail in your application code, you hand the raw email to PowerMTA, and it signs it right before delivery. This saves CPU cycles on your application layer. sample powermta configuration file hot
<source 127.0.0.1> always-allow-relaying yes Use code with caution. Copied to clipboard Key Directives Explained <pickup-directory [path]>
: Specifies the absolute path where PMTA will look for new message files. virtual-mta : Assigns the mail dropped in this folder to a specific VirtualMTA (IP pool and domain settings) for delivery. scan-interval
: Sets how often (in seconds) PMTA checks the folder for new files. delete-after-read : If set to
, PMTA removes the file from the hot folder once it has been moved into the internal delivery spool. Best Practices for Implementation File Permissions : Ensure the user has read and write permissions for the specified path. Atomic Writes
: Always write files to a temporary directory first and then
them into the hot folder. This prevents PMTA from attempting to read a partially written file. Avoid Disk Bottlenecks
: If sending millions of emails, use a high-performance disk (like an SSD or NVMe) or a RAM-disk to prevent I/O wait times from slowing down the injection. Exclusion from Scanning
: Ensure anti-virus or indexing services do not scan the pickup folder, as they can lock files and cause PMTA to fail. configure VirtualMTAs to work specifically with these pickup directories? Day 8 : Hot Folder Configuration - Priyanka Manikkoth In PowerMTA (PMTA), a "hot" configuration generally refers
adaptive-throttling yes min-backoff 30s max-backoff 24h backoff-scale-factor 1.5
<domain> DirectivesThis is the heart of PowerMTA.
max-msg-rate: If you send 1,000 emails a second to Gmail, they will block your IP in a heartbeat. This setting throttles your output to match what the receiver tolerates.max-smtp-out: This limits concurrent connections. Think of it as not trying to shove too many people through a single doorway at once.While not in the config file text above, a truly "hot" configuration requires external setup:
This article provides a comprehensive, high-performance "hot" configuration for PowerMTA (PMTA). When we say a configuration is "hot," we mean it is optimized for high-volume throughput, excellent deliverability, and real-time bounce/FBL handling.
Below is a breakdown of a production-ready config file, followed by an explanation of the critical directives. Sample PowerMTA "Hot" Configuration File
# ########################################################### # PowerMTA High-Performance Configuration (The "Hot" Setup) # ########################################################### # --- 1. IP and Networking --- # Define the IP addresses you will use for sending smtp-source-host 1.2.3.4 ://yourdomain.com smtp-source-host 1.2.3.5 ://yourdomain.com # --- 2. Postmaster and Logging --- postmaster postmaster@yourdomain.com Use code with caution. Why This Configuration is "Hot" 1. Granular Domain Directives
The "hot" secret to PowerMTA is not treating every recipient the same. Gmail, Yahoo, and Outlook have vastly different spam filtering thresholds. By splitting them into
Notice the dkim-sign yes directive. In the modern email landscape, unsigned mail is often discarded immediately. This config assumes you have your private keys mapped, ensuring every outbound packet is authenticated. 3. Optimized Virtual MTAs (vmta)
By grouping IPs into virtual-mta pools, you can rotate your sending identity. If one IP gets "cold" (low reputation), you can shift traffic to another pool without rewriting your entire application logic. 4. Advanced Bounce Handling Throttling & Delivery Rules
<domain hotmail
The
By explicitly defining smtp-source-host, you ensure that PowerMTA binds to the correct local IP. This is vital for multi-IP servers to ensure that the Reverse DNS (rDNS) always matches the IP address being used. Best Practices for Deployment
Warm-up: Even with this "hot" config, start your max-msg-rate low (e.g., 50/hour) and double it every 48 hours if your bounce rates remain under 1%.
Monitoring: Use the http-mgmt-port (8080 in the sample) to watch your queues in real-time. If you see a "backoff" status, lower your max-smtp-out immediately.
Disk I/O: For truly high-performance setups, ensure your PowerMTA spool directory is on an NVMe SSD to prevent bottlenecks during massive bursts.
In PowerMTA (PMTA), "hot folders" (often referred to as pickup directories
) allow you to inject emails for delivery by simply dropping message files into a specific folder on the server.
This configuration is ideal for high-volume automated systems that need to bypass the overhead of a full SMTP session. Sample Configuration for a Pickup Directory (Hot Folder) To enable a pickup directory, you must define a
# Define the pickup directory (hot folder)
# Frequency in seconds to scan the folder
scan-interval 5
# Delete files after they are successfully read
delete-after-read yes