EmailPlugin: Allow Email SMTP settings per channel

[martijnvdbrug]

Is your feature request related to a problem? Please describe.
I would like to be able to have different SMTP settings per channel, preferably stored in the database, so that administrators can configure their own mail server.

Describe the solution you'd like
My initial thought is to transform the transport property in the EmailPlugin.init() to a function, so that developers can dictate where SMTP settings are coming from:

    EmailPlugin.init({
      transport: async (ctx) => {

        // Get your SMTP settings based on the requestContext
        const settings = await myService.getSmtpSettings(ctx);

          return {
            type: 'smtp',
            host: settings.host,
            port: settings.port,
            auth: {
              user: settings.user,
              pass: settings.password,
            }
          }
          ...
    })

This way we can, for example, get SMTP config stored on custom fields on a Channel

Describe alternatives you've considered
I am currently using a transactional mail service, that also enables me to send emails from different domains with a single SMTP connection, which works fine, but all channels are forced to use the same transactional email service.

I would like to hear your thoughts on this. Is this something that should be included in Vendure, or is this a use case for a separate plugin?

Additional context

The process function is already async, so it shouldn't be to hard to resolve transport settings here:

vendure/packages/email-plugin/src/email-processor.ts

Line 77 in 7b0fae1

await this.emailSender.send(emailDetails, this.transport);

[martijnvdbrug]

For future reference @is0utfitters

[michaelbromley]

Yes this proposal seems reasonable. We would also need to expose an injector instance so that you can inject your services into the method.

[martijnvdbrug]

Thanks for the response, can you assign this to me?