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Version: 0.16

General

General server settings are grouped on the SystemSettings singleton (found in the WebUI under Settings › Network › Services, Settings › Network › General). This page covers the hostname, the CPU thread pool, and IP address allow / block lists. Per-listener concurrency is described on the Listeners page.

Server hostname​

The default server hostname is used in SMTP EHLO commands, in message headers, and in reports. It is configured through defaultHostname on the SystemSettings singleton. If the field is left unset, the server falls back to the hostname reported by the operating system.

Thread pool size​

Stalwart runs CPU-intensive tasks on a dedicated thread pool. The pool size is controlled by threadPoolSize on the SystemSettings singleton. When left unset, the server allocates one worker per CPU core detected at start-up. Raising the value above the number of available cores does not generally improve throughput.

IP address blocking​

IP addresses and ranges can be rejected at connection time. Each blocked entry is represented by a BlockedIp record (found in the WebUI under Settings › Security › Blocked IPs); the address field accepts a single IP address or a CIDR mask such as 203.0.113.0/24, and expiresAt can be set to make the block temporary.

When auto-banning is enabled, the server creates BlockedIp records automatically for sources that exceed the configured thresholds. Manual entries can be managed from the WebUI or the CLI.

IP address allow list​

IP addresses and ranges that should bypass rate limits and auto-banning are represented by AllowedIp records (found in the WebUI under Settings › Security › Allowed IPs). The address field accepts a single IP address or a CIDR mask, and expiresAt can be used for time-bounded allowances. The localhost addresses 127.0.0.1 and ::1 are allowed by default to prevent accidental lockouts.

Run as user​

On Linux systems, Stalwart requires the CAP_NET_BIND_SERVICE capability to bind to privileged ports (those below 1024). On older systems that do not support this capability, Stalwart can be started as root and then drop privileges to a non-privileged account. The target user and group are selected through the RUN_AS_USER and RUN_AS_GROUP environment variables.