docs: note that subdomains need Email Routing enabled separately (#970)

Subdomains do not inherit Email Routing from the apex domain;
each subdomain must enable Email Routing and configure its own
DNS records and Catch-all rule.

Refs #969

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

vitepress-docs/docs/en/guide/common-issues.md

@@ -9,6 +9,7 @@
 | ------------------------------------------------------ | ------------------------------------------------------------------------------------------------- |
 | Sending emails to authenticated forwarding addresses using Cloudflare Workers | Use CF's API for sending, only supports recipient addresses bound to CF, i.e., CF EMAIL forwarding destination addresses |
 | Binding multiple domains                               | Each domain needs to configure email forwarding to worker                                         |
+| Subdomain cannot receive email                         | Subdomains must have Email Routing **enabled separately** on Cloudflare with their own DNS records and Catch-all rule. Enabling it only on the apex domain does NOT cover subdomains. See [Email Routing](/en/guide/email-routing) |
 
 ## Worker Related
 

vitepress-docs/docs/en/guide/email-routing.md

@@ -7,3 +7,6 @@
 3. Configure the `Catch-all address` in the routing rules of each domain's `Email Routing` to send to `worker`.
 
 ![email](/readme_assets/email.png)
+
+> [!WARNING] Subdomains must be configured separately
+> If you want to receive mail on a **subdomain** (e.g. `mail.example.com`), you must enable `Email Routing` on **that subdomain** in the CF dashboard and configure its email DNS records and Catch-all rule separately. Enabling Email Routing only on the apex domain **does not cover subdomains**.

vitepress-docs/docs/zh/guide/common-issues.md

@@ -9,6 +9,7 @@
 | -------------------------------------------------- | ------------------------------------------------------------------------------- |
 | 使用 Cloudflare Workers 给已认证的转发邮箱发送邮件 | 使用 cf 的 API 进行发送，只支持绑定到 CF 上的收件地址，即 CF EMAIL 转发目的地址 |
 | 绑定多个域名                                       | 每个域名都需要设置 email 转发到 worker                                          |
+| 子域名收不到邮件                                   | 子域名需要在 CF 上**单独启用** Email Routing 并配置 DNS 与 Catch-all 规则，仅在一级域开启不会自动覆盖子域，详见 [Email Routing](/zh/guide/email-routing) |
 
 ## Worker 相关
 

vitepress-docs/docs/zh/guide/email-routing.md

@@ -7,3 +7,6 @@
 3. 配置每个域名的 `Email Routing` 的路由规则中的  `Catch-all 地址` 发送到 `worker`
 
 ![email](/readme_assets/email.png)
+
+> [!WARNING] 子域需要单独配置
+> 如果你要用**子域名**（如 `mail.example.com`）收信，必须在 CF 控制台里对 **该子域** 单独启用 `Email Routing`，并配置邮件 DNS 记录与 Catch-all 规则。仅在一级域名上开启 Email Routing **不会自动覆盖子域名**。