Postal v3 fails to forward messages to SMTP servers

[amplitudesxd]

Describe the bug

Incoming emails via Postal cannot be forwarded to SMTP servers. The error "An internal error occurred while sending this message. This message will be retried automatically." is displayed.

To Reproduce

1. Setup the latest version of Postal
2. Create an SMTP endpoint
3. Create a route and assign to the SMTP endpoint

Expected behaviour

I expect Postal to forward the message, like it does on v2.

Additional information/context

NoMethodError: undefined method `endpoints' for #<SMTPEndpoint id: 3, server_id: 14, uuid: "fe5778de-12af-4a22-aa0c-575468dbae41", name: "Google SMTP", hostname: "smtp.google.com", ssl_mode: "Auto", port: nil, error: nil, disabled_until: nil, last_us