Centralized Email/SMPT Configuration via Relay Service

[TheBrambleShark]

Hi all,

Working on my first Aspire app and I'm finding that I have multiple components that need to send emails. For instance, KeyCloak needs to send emails when users register or use some sort of self service management (e.g. password resets) and my main app has the ability to email reports. While that's only two services currently, it's a good representation of what may occur in a real life scenario.

Perhaps this issue is somewhat resolved when hosting in the cloud, e.g. with Azure, but I also believe that there is a place for Aspire in on-premises deployments (read as "your own cloud").

I'm creating this post as a sort of discussion for how to go about centralized email configuration. The main goal of this discussion is to discuss a scheme which will prevent needing to configure and maintain SMTP configurations across multiple orchestrated services, but still allow the flexibility of enabling users to choose different configurations per-service.

Possibly the easiest way to accomplish this would be to add some sort of containerized email relay, then configure services to publish to that relay. The person who deploys the Aspire app then only needs to configure the email relay and it should just work™️.

A few open questions remain:

• How can we provide this information to non-dotnet services orchestrated by Aspire?
  • Some allow for configuration via environment variables. If that's the case, this is easily solved using .WithEnvironment(string, string).
  • Some require a configuration file to be set. I'm not sure if there's some file manager that can handle writing/updating these configuration files.
• Should this email service provide testing facilities, such as what MailPit provides?
• How do we secure this service?
  • It definitely should NOT be exposed publicly (let's avoid hosting open mail relays).
  • Can we add HTTPS support by reusing the development certificate/accepting a specified certificate in production?

Any thoughts/ideas/questions welcome!

[TheBrambleShark]

Related: #4063