IMAP Server


Stalwart IMAP supports both the IMAP4rev2 and IMAP4rev1 protocols as well as numerous extensions. Clients can connect to Stalwart IMAP over two ports; a TLS encrypted port and a clear-text port which supports TLS connection upgrades. This section covers the basic IMAP server configuration.

Bind address

The bind address is where Stalwart IMAP will listen for incoming IMAP4 requests. It is configured with the bind-addr, bind-port and bind-port-tls parameters:

  • bind-addr: IP address to bind the IMAP service to, or specify to bind to all network interfaces. Defaults to
  • bind-port: Port to listen for clear text IMAP connections, defaults to 143. Connections can later be upgraded to TLS with the STARTTLS IMAP command.
  • bind-port-tls: Port to listen for TLS IMAP connections, defaults to 993.


bind-port: 143
bind-port-tls: 993


Transport Layer Security (TLS) is a cryptographic protocol designed to provide communications security over a computer network. TLS should be enabled in Stalwart IMAP to keep your users’ information secure, otherwise clear-text authentication mechanisms such as AUTH=PLAIN or LOGIN will not be offered to clients.

The parameters cert-path and key-path specify the path to the TLS certificate and private key respectively. For example:

cert-path: /usr/local/stalwart-imap/etc/imap.crt
key-path: /usr/local/stalwart-imap/etc/imap.key

If you currently don’t have a TLS certificate, you can obtain one for free from Let’s Encrypt.


The logging level is configured with the log-level parameter which accepts the following values:

  • error: Only log very serious errors.
  • warn: Log hazardous situations in addition to serious errors.
  • info: Log useful information plus all kind of errors.
  • debug: Log lower priority information useful to debug problem.
  • trace: Log everything including very low priority, often extremely verbose, information.

The default logging level is info. Example:

log-level: info

Request Size

The maximum size of an IMAP request is controlled with the max-request-size parameter. This number has to be large enough to allow users to import messages using the APPEND command. The default value is 52428800 bytes (50MB). Example:

max-request-size: 52428800

Worker Pool

On startup Stalwart IMAP creates a thread pool where blocking tasks are executed. By default the number of threads started equals the number of CPUs in the system. The size of the thread pool can be changed using the worker-pool-size, for example:

worker-pool-size: 16