Postfix/main.cf

About
main.cf is the main configuration file for Postfix. The official documentation for the file's format is in man 5 postconf and on postfix.org.

Syntax
Earlier values are overridden by later values.

Options

 * /alias_maps
 * /mailbox_command
 * /mailbox_transport
 * /receive_override_options
 * /sender_bcc_maps
 * /smtp_sasl_auth_enable - enable authentication from local SMTP client to external SMTP relay server
 * /smtpd_sasl_auth_enable
 * /virtual_mailbox_domains
 * /virtual_mailbox_maps
 * /virtual_transport

Reference

 * official