The software fails to honor the `disableFileAccess` and `disableUrlAccess` sandbox options when message content is resolved through the public plugin API `MailMessage.resolveContent()` using the legacy three-argument signature `resolveContent(data, key, callback)`. This occurs because `shared.resolveContent()` normalizes the missing `options` argument to an empty object, causing the `resolveContentValue()` function to skip access-control checks and reach `nmfetch(url)` or `fs.createReadStream(path)`. Consequently, application or plugin code resolving untrusted content (such as html, text, attachment `path`, or `href`) can be manipulated to read arbitrary local files or perform server-side request forgery (SSRF), which is when an attacker induces a server to make requests to an unintended location, bypassing the enabled sandbox.