How to handle email delivery failures

[denvaar]

I am using Bamboo to send account confirmation emails when someone creates an account. I'm using deliver_later to send emails in the background. In my application, an account is initially created as "inactive" until they use the confirmation link in the email.

I want to be able to handle the case where a fake email is used to create an account, because I don't want a bunch of fake stuff hanging around in the database. My application doesn't know it's fake until this exception is raised from within a different process:

(Bamboo.SMTPAdapter.SMTPError) There was a problem sending the email through SMTP

I looked at the docs and came up with a solution using a custom delivery strategy, but I am not sure if this type of thing is what it's intended for, so I wanted to get some validation, and check if this is a good thing to do. As you can see from my code below, I am basically just catching the exception and then deleting the fake user account from the database.

defmodule MyApp.AsyncEmailStrategey do
  @behaviour Bamboo.DeliverLaterStrategy

  alias MyApp.Accounts

  def deliver_later(adapter, email, config) do
    Task.async fn ->
      try do
        adapter.deliver(email, config)
      rescue
        error in Bamboo.SMTPAdapter.SMTPError ->
          remove_user_account(email)
          raise error
      end
    end
  end

  defp remove_user_account(email) do
    with [nil: bad_email] = email.to,
         user = Accounts.get_user_by_email(bad_email)
    do
      Accounts.delete_user(user)
    end
  end
end

[claytongentry]

Would like to bump this issue.

We have tested a similar try / rescue flow using Amazon SES Simulator inbox addresses and have found the adapter does not raise as we'd expect on deliveries to the faulty addresses, e.g. bounce@simulator.amazonses.com.

This makes it difficult to clean our lists of bouncing, suppressed or complaint emails.

[claytongentry]

Hey @denvaar, don't know if you're still having this issue but if on the off-chance you happen to be using SES, the solution we ended up going with is subscribing to bounce and complaint notifications via SNS.

https://docs.aws.amazon.com/ses/latest/DeveloperGuide/notifications-via-sns.html

[blacksph3re]

Still it would be nice having this for any smtp service which doesn't support separate bounce/complaint notifications

[germsvel]

I know it's been a while since this issue was opened. But I wanted to drop a note since there were some changes in Bamboo 2 that might be helpful.

With Bamboo 2.0.0, deliver_now doesn't raise errors on failure — and therefore adapters shouldn't raise errors on adapter.deliver. So I think having something like @denvaar originally posted makes sense, except now you don't have to catch an exception. You can use a case statement and pattern match on {:error, error} instead:

defmodule MyApp.AsyncEmailStrategey do
  @behaviour Bamboo.DeliverLaterStrategy

  alias MyApp.Accounts

  def deliver_later(adapter, email, config) do
    Task.async fn ->
      case adapter.deliver(email, config) do
        {:ok, _} -> # success
        {:error, error} -> remove_user_account(email)
      end
    end
  end
end

I think that is a good way to handle email delivery failures. So I'll go ahead and close this issue. If others think it should still be open, I'd be happy to reopen it.