Module ngx_mail_ssl_module

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2023-12-01

The ngx_mail_ssl_module provides the necessary support for mail proxy server for the SSL/TLS protocol.

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

This module requires the OpenSSL library.

Directives

syntax:	`ssl on \| off;`
default:	ssl off;
context:	`mail`, `server`

Enables the SSL/TLS protocol for the given server.

syntax:	`ssl_certificate file;`
default:	—
context:	`mail`, `server`

Specifies a file with a certificate in the PEM format for the given server. If intermediate certificates should be specified in addition to a primary certificate, they should be specified in the same file in the following order: the primary certificate comes first, then the intermediate certificates. A secret key in the PEM format may be placed in the same file.

syntax:	`ssl_certificate_key file;`
default:	—
context:	`mail`, `server`

Specifies a file with a secret key in the PEM format for the given server.

syntax:	`ssl_prefer_server_ciphers on \| off;`
default:	ssl_prefer_server_ciphers off;
context:	`mail`, `server`

Specifies that server ciphers should be preferred over client ciphers when using the SSLv3 and TLS protocols.

syntax:	`ssl_protocols [SSLv2] [SSLv3] [TLSv1] [TLSv1.1] [TLSv1.2];`
default:	ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
context:	`mail`, `server`

Enables the specified protocols. The parameters TLSv1.1 and TLSv1.2 work only when using the OpenSSL library version 1.0.1 and higher.

The parameters TLSv1.1 and TLSv1.2 are supported starting from versions 1.1.13 and 1.0.12 so when using OpenSSL version 1.0.1 and higher on older nginx versions these protocols will work but could not be disabled.

syntax:	`ssl_session_cache off \| none \| [builtin[:size]] [shared:name:size];`
default:	ssl_session_cache none;
context:	`mail`, `server`

Sets types and sizes of caches that store session parameters. A cache can be any of the following types:

off: the use of session cache is strictly prohibited: nginx explicitly tells a client that sessions may not be reused.
none: the use of session cache is gently disallowed: nginx tells a client that sessions may be reused, but does not actually do that.
builtin: a cache built in OpenSSL; used by one worker process only. The cache size is specified in sessions. If size is not given, it is equal to 20480 sessions. Use of the built-in cache can cause memory fragmentation.
shared: shared between all worker processes. The cache size is specified in bytes; one megabyte can store about 4000 sessions. Each shared cache should have an arbitrary name. A cache with the same name can be used in several servers.

Both cache types can be used simultaneously, for example:

ssl_session_cache builtin:1000 shared:SSL:10m;

but using only shared cache without the built-in cache should be more efficient.

syntax:	`ssl_session_timeout time;`
default:	ssl_session_timeout 5m;
context:	`mail`, `server`

Specifies a time during which a client may reuse the session parameters stored in a cache.

syntax:	`starttls on \| off \| only;`
default:	starttls off;
context:	`mail`, `server`

on: Allow usage of STLS command for the POP3 and STARTTLS command for the IMAP;
off: Deny usage of STLS and STARTTLS commands;
only: require preliminary TLS transition.