doc: added description for SMTP

Author: arianpotter

apps/public/content/docs/self-hosting/environment-variables.mdx

@@ -324,15 +324,81 @@ Get your API key from [resend.com](https://resend.com). Make sure to verify your
 **Required**: No  
 **Default**: `hello@openpanel.dev`
 
-Email address used as the sender for transactional emails.
+Email address used as the sender for transactional emails. Applies to both Resend and SMTP transports.
 
 **Example**:
 ```bash
 EMAIL_SENDER=noreply@yourdomain.com
 ```
 
+### SMTP_HOST
+
+**Type**: `string`  
+**Required**: No  
+**Default**: None
+
+SMTP server hostname. When set, OpenPanel uses SMTP to send emails instead of Resend. Takes priority over `RESEND_API_KEY` if both are configured.
+
+**Example**:
+```bash
+SMTP_HOST=smtp.example.com
+```
+
+### SMTP_PORT
+
+**Type**: `number`  
+**Required**: No  
+**Default**: `587`
+
+SMTP server port.
+
+**Example**:
+```bash
+SMTP_PORT=587
+```
+
+### SMTP_SECURE
+
+**Type**: `boolean`  
+**Required**: No  
+**Default**: `false`
+
+Use TLS for the SMTP connection. Set to `true` when using port `465`.
+
+**Example**:
+```bash
+SMTP_SECURE=true
+```
+
+### SMTP_USER
+
+**Type**: `string`  
+**Required**: No  
+**Default**: None
+
+SMTP authentication username. Leave unset if your server does not require authentication.
+
+**Example**:
+```bash
+SMTP_USER=smtp-user@example.com
+```
+
+### SMTP_PASS
+
+**Type**: `string`  
+**Required**: No  
+**Default**: None
+
+SMTP authentication password.
+
+**Example**:
+```bash
+SMTP_PASS=your-smtp-password
+```
+
 <Callout>
-The sender email must be verified in your Resend account.
+Set `SMTP_HOST` to enable SMTP. If both `SMTP_HOST` and `RESEND_API_KEY` are present, SMTP takes priority. If neither is set, emails are logged to the console (useful for development).
+In case of using Resend, the sender email must be verified in your Resend account.
 </Callout>
 
 ## OAuth & Integrations
@@ -834,7 +900,7 @@ For a basic self-hosted installation, these variables are required:
 
 ### Optional but Recommended
 
-- `RESEND_API_KEY` - For email features
+- `RESEND_API_KEY` or `SMTP_HOST` - For email features (pick one)
 - `EMAIL_SENDER` - Email sender address
 - `OPENAI_API_KEY` and/or `ANTHROPIC_API_KEY` - For the in-app AI chat assistant
 

apps/public/content/docs/self-hosting/self-hosting.mdx

@@ -102,7 +102,7 @@ const op = new OpenPanel({
 
 ### E-mail
 
-Some of OpenPanel's features require e-mail. We use Resend as our transactional e-mail provider. To enable email features, create an account on Resend and set the `RESEND_API_KEY` environment variable.
+Some of OpenPanel's features require e-mail. We use Resend as our transactional e-mail provider by default, but you can also use your own SMTP server. To enable email features, set the relevant environment variables described below.
 
 <Callout>This is nothing that is required for the basic setup, but it is required for some features.</Callout>
 
@@ -112,6 +112,32 @@ Features that require e-mail:
 - Invitations
 - more will be added over time
 
+#### Option A — Resend
+
+Create an account on [resend.com](https://resend.com), verify your sender domain, and set the `RESEND_API_KEY` environment variable.
+
+```bash title=".env"
+RESEND_API_KEY=re_xxxxxxxxxxxxx
+EMAIL_SENDER=noreply@yourdomain.com
+```
+
+#### Option B — SMTP
+
+If you prefer to use your own SMTP server, set `SMTP_HOST` and OpenPanel will use it instead of Resend.
+
+```bash title=".env"
+SMTP_HOST=smtp.example.com
+SMTP_PORT=587
+SMTP_SECURE=false
+SMTP_USER=smtp-user@example.com
+SMTP_PASS=your-smtp-password
+EMAIL_SENDER=noreply@yourdomain.com
+```
+
+<Callout type="info">
+`SMTP_HOST` takes priority over `RESEND_API_KEY` if both are set. If neither is configured, emails are logged to the console instead of being sent.
+</Callout>
+
 For email configuration details, see the [Environment Variables documentation](/docs/self-hosting/environment-variables#email).
 
 ### AI integration