postconf: add page (#10784)

* Adding page for postconf command

* Adding trailing colon

* addressed comments

* addressed comments

pages/linux/postconf.md

@@ -0,0 +1,29 @@
+# postconf
+
+> Postfix configuration utility.
+> This command displays the values of the `main.cf` configuration parameters by default and warns about possible mistyped parameter names. It can also change the `main.cf` configuration parameter values.
+> More information: <https://manned.org/postconf>.
+
+- Specify the directory of the `main.cf` configuration file instead of the default configuration directory:
+
+`postconf -c {{path/to/configuration_directory}}`
+
+- Edit the `main.cf` configuration file and update parameter settings with the "name=value" pairs:
+
+`postconf -e`
+
+- Print the default parameter settings of the `main.cf` instead of the actual settings:
+
+`postconf -d`
+
+- Display parameters only from the specified class. The class can be one of builtin, service, user or all:
+
+`postconf -C {{class}}`
+
+- List available SASL plug-in types for the Postfix SMTP server. The plug-in type is selected with the `smtpd_sasl_type` configuration parameter by specifying `cyrus` or `dovecot` as the name:
+
+`postconf -a`
+
+- List the names of all supported lookup table types. Lookup tables are specified as `type:name` in configuration files where the type can be `btree`, `cdb`, `hash`, `mysql`, etc:
+
+`postconf -m`