feat: configurable trusted proxies for web requests

doc/config/environment-variables.md

@@ -17,6 +17,7 @@ This document contains all the environment variables which are available for thi
 | `POSTAL_USE_RESENT_SENDER_HEADER` | Boolean | Append a Resend-Sender header to all outgoing e-mails | true |
 | `POSTAL_SIGNING_KEY_PATH` | String | Path to the private key used for signing | config/postal/signing.key |
 | `POSTAL_SMTP_RELAYS` | Array of strings | An array of SMTP relays in the format of smtp://host:port |  |
+| `POSTAL_TRUSTED_PROXIES` | Array of strings | An array of IP addresses to trust for proxying requests to Postal (in addition to localhost addresses) |  |
 | `WEB_SERVER_DEFAULT_PORT` | Integer | The default port the web server should listen on unless overriden by the PORT environment variable | 5000 |
 | `WEB_SERVER_DEFAULT_BIND_ADDRESS` | String | The default bind address the web server should listen on unless overriden by the BIND_ADDRESS environment variable | 127.0.0.1 |
 | `WEB_SERVER_MAX_THREADS` | Integer | The maximum number of threads which can be used by the web server | 5 |