[Feature Request] ability to set custom smtp body/title

I need the ability to send a specially crafted smtp message to interface with an smtp api of an external service.

For example, I want to be able to configure an email body template like this:

``` json
"smtp": {
"from": "beacon@fake_company.com",
"to": ["sms_api@externalservice.com"],
"body": "user: fake_company\n
password: b4dp4ssw0rD\n
api_key: Ishoquu7teis8ahFeeshae2gae2quahchoa0koom\n
to: +9055533322, +304512547895\n
sms_body: \n
$level - $name\n
$target\n
- sent from beacon"
}
```

Start by locating the SMTP configuration and message-construction entry points; the issue provides a JSON example with custom recipients, body content, and template variables. Determine how custom body and title templates should be configured and verify that the generated SMTP message matches the external service's expected format.

Written by the indexing model from the issue text.