Mailcow - Create Noreply Mailbox

Steps

First create a mailbox as you usually do. There is nothing special there.

Then, as the admin, go to the Filters tab and then click Add Filter.

1. Select the mailbox that will act as a noreply mailbox.
2. Ensure the filter is set to Prefilter.
3. Give this filter a description to see it by in the overview page later.
4. Input the following code:

require ["reject"];
reject "This mailbox does not accept emails.";

Now when you send an email to that mailbox, you should get an automatic rejected response as shown below:

If you open the rejection email, you will see something like below:

Conclusion

You have now configured a noreply mailbox, such that if anybody sends an email to it, it will automatically get rejected and thrown away, but more importantly, the user is notified that the email was rejected and will not be read.