Module ngx_mail_core_module

This module is not built by default, it should be enabled with the --with-mail configuration parameter.

worker_processes auto;

error_log /var/log/nginx/error.log info;

events {
    worker_connections  1024;
}

mail {
    server_name       mail.example.com;
    auth_http         localhost:9000/cgi-bin/nginxauth.cgi;

    imap_capabilities IMAP4rev1 UIDPLUS IDLE LITERAL+ QUOTA;

    pop3_auth         plain apop cram-md5;
    pop3_capabilities LAST TOP USER PIPELINING UIDL;

    smtp_auth         login plain cram-md5;
    smtp_capabilities "SIZE 10485760" ENHANCEDSTATUSCODES 8BITMIME DSN;
    xclient           off;

    server {
        listen   25;
        protocol smtp;
    }
    server {
        listen   110;
        protocol pop3;
        proxy_pass_error_message on;
    }
    server {
        listen   143;
        protocol imap;
    }
    server {
        listen   587;
        protocol smtp;
    }
}

Sets the address and port for the socket on which the server will accept requests. It is possible to specify just the port. The address can also be a hostname, for example:

listen 127.0.0.1:110;
listen *:110;
listen 110;     # same as *:110
listen localhost:110;

IPv6 addresses (0.7.58) are specified in square brackets:

listen [::1]:110;
listen [::]:110;

UNIX-domain sockets (1.3.5) are specified with the “unix:” prefix:

listen unix:/var/run/nginx.sock;

Different servers must listen on different address:port pairs.

The ssl parameter allows specifying that all connections accepted on this port should work in SSL mode.

The proxy_protocol parameter (1.19.8) allows specifying that all connections accepted on this port should use the PROXY protocol. Obtained information is passed to the authentication server and can be used to change the client address.

The listen directive can have several additional parameters specific to socket-related system calls.

backlog=number

sets the backlog parameter in the listen() call that limits the maximum length for the queue of pending connections (1.9.2). By default, backlog is set to -1 on FreeBSD, DragonFly BSD, and macOS, and to 511 on other platforms.

rcvbuf=size

sets the receive buffer size (the SO_RCVBUF option) for the listening socket (1.11.13).

sndbuf=size

sets the send buffer size (the SO_SNDBUF option) for the listening socket (1.11.13).

bind

this parameter instructs to make a separate bind() call for a given address:port pair. The fact is that if there are several listen directives with the same port but different addresses, and one of the listen directives listens on all addresses for the given port (*:port), nginx will bind() only to *:port. It should be noted that the getsockname() system call will be made in this case to determine the address that accepted the connection. If the backlog, rcvbuf, sndbuf, ipv6only, or so_keepalive parameters are used then for a given address:port pair a separate bind() call will always be made.

ipv6only=on|off

this parameter determines (via the IPV6_V6ONLY socket option) whether an IPv6 socket listening on a wildcard address [::] will accept only IPv6 connections or both IPv6 and IPv4 connections. This parameter is turned on by default. It can only be set once on start.

so_keepalive=on|off|[keepidle]:[keepintvl]:[keepcnt]

this parameter configures the “TCP keepalive” behavior for the listening socket. If this parameter is omitted then the operating system’s settings will be in effect for the socket. If it is set to the value “on”, the SO_KEEPALIVE option is turned on for the socket. If it is set to the value “off”, the SO_KEEPALIVE option is turned off for the socket. Some operating systems support setting of TCP keepalive parameters on a per-socket basis using the TCP_KEEPIDLE, TCP_KEEPINTVL, and TCP_KEEPCNT socket options. On such systems (currently, Linux 2.4+, NetBSD 5+, and FreeBSD 9.0-STABLE), they can be configured using the keepidle, keepintvl, and keepcnt parameters. One or two parameters may be omitted, in which case the system default setting for the corresponding socket option will be in effect. For example,

so_keepalive=30m::10

will set the idle timeout (TCP_KEEPIDLE) to 30 minutes, leave the probe interval (TCP_KEEPINTVL) at its system default, and set the probes count (TCP_KEEPCNT) to 10 probes.

Provides the configuration file context in which the mail server directives are specified.

max_commands 1000;

Sets the maximum number of commands allowed during authentication. If the limit is reached and proxying to the backend is not started yet, the connection is closed.

max_errors 5;

Sets the number of protocol errors after which the connection is closed.

Sets the protocol for a proxied server. Supported protocols are IMAP, POP3, and SMTP.

If the directive is not set, the protocol can be detected automatically based on the well-known port specified in the listen directive:

• imap: 143, 993
• pop3: 110, 995
• smtp: 25, 587, 465

Unnecessary protocols can be disabled using the configuration parameters --without-mail_imap_module, --without-mail_pop3_module, and --without-mail_smtp_module.

resolver off;

Configures name servers used to find the client’s hostname to pass it to the authentication server, and in the XCLIENT command when proxying SMTP. For example:

resolver 127.0.0.1 [::1]:5353;

The address can be specified as a domain name or IP address, with an optional port (1.3.1, 1.2.2). If port is not specified, the port 53 is used. Name servers are queried in a round-robin fashion.

Before version 1.1.7, only a single name server could be configured. Specifying name servers using IPv6 addresses is supported starting from versions 1.3.1 and 1.2.2.

By default, nginx will look up both IPv4 and IPv6 addresses while resolving. If looking up of IPv4 or IPv6 addresses is not desired, the ipv4=off (1.23.1) or the ipv6=off parameter can be specified.

Resolving of names into IPv6 addresses is supported starting from version 1.5.8.

By default, nginx caches answers using the TTL value of a response. An optional valid parameter allows overriding it:

resolver 127.0.0.1 [::1]:5353 valid=30s;

Before version 1.1.9, tuning of caching time was not possible, and nginx always cached answers for the duration of 5 minutes.

To prevent DNS spoofing, it is recommended configuring DNS servers in a properly secured trusted local network.

The special value off disables resolving.

resolver_timeout 30s;

Sets a timeout for DNS operations, for example:

resolver_timeout 5s;

Sets the configuration for a server.

server_name hostname;

Sets the server name that is used:

• in the initial POP3/SMTP server greeting;
• in the salt during the SASL CRAM-MD5 authentication;
• in the EHLO command when connecting to the SMTP backend, if the passing of the XCLIENT command is enabled.

If the directive is not specified, the machine’s hostname is used.

timeout 60s;

Sets the timeout that is used before proxying to the backend starts.