Update README.md

added POSTFIX_RELAY_ENCRYPTION description.

README.md

@@ -165,8 +165,9 @@ linux/arm64
 * `POSTFIX_RELAYHOST_AUTH_ENABLE`: Enable client-side authentication for relayhost (default `false`)
 * `POSTFIX_RELAYHOST_USERNAME`: Postfix SMTP Client username for relayhost authentication
 * `POSTFIX_RELAYHOST_PASSWORD`: Postfix SMTP Client password for relayhost authentication
+* `POSTFIX_RELAY_ENCRYPTION`: Set to `SSL` to enable SSL encrpytion over SMTP where TLS is not available.
 * `POSTFIX_SPAMHAUS_DQS_KEY`: Personal key for [Spamhaus DQS](#spamhaus-dqs-configuration)
-
+* 
 > [!NOTE]
 > `POSTFIX_RELAYHOST_USERNAME_FILE` and `POSTFIX_RELAYHOST_PASSWORD_FILE` can be
 > used to fill in the value from a file, especially for Docker's secrets feature.