To Many Requests

I provided a solution via the issue fork, here also a patch for this solution.

This seems like a good idea. I just took a quick look and need to go through it in more detail, but I think we can probably implement \Drupal\Core\Queue\DelayableQueueInterface and use that to handle the delaying of queue items.

That is possible indeed when you always use the queue for sending the mails. But if that option isn't checked we cannot use it. That's why I create a new queue item.

Does this still happen with the dev release without the patch applied?

We've previously hit "too many requests" in 🐛 Throttle code causes rate limit warnings Fixed on the API because the module made a request to check the quota (so it could calculate the send delay) before each email. In our case the problem didn't happen because there were too many actual *emails* being sent.