Send by email a message to add it in a topic

We can create topics by email or reply to a notification by email but it seems impossible to add a message to a topic with a unique email address. I explored the forum to understand all features related to emails:

My use case : we have an email address to create topic by email like something@mydiscourse.com in a private category. Only two groups can access to this category and receive a notification for each new topics. Members can reply by email to join the topic. It’s like an internal mailing list to initiate topics and engage only members that want to contribute.

I want to engage external persons that are not registered users. I write an email to johndoe@another-organization.org and janedoe@example.com. To create a topic in the private category and keep an history of all future replies (from external and from members), I try this configuration:

  1. put in copy something@mydiscourse.com
  2. accept emails from anonymous users with no accounts in the category
  3. disable find related post with key

But:

  1. It’s not recommanded to disable find related post with key
  2. it does not work : I got the error topic not found in mail logs

I think, it should be interested to associate a email address to a topic with a reply key. Each member could be copy the email address and put it in copy. So all replies would be added to the topic.

This feature would be interesting to:

  1. Share content by email in permanent topics
  2. Engage external user in an existing topic