Summary

Notifications triggered via the Jira REST API will have the "reply-to" header as the user who triggered the notification instead of Jira's mail server (jira@instance.atlassian.net). This will cause email replies to go directly to the user, instead of adding a comment to the ticket.

Steps to Reproduce

1. In a Jira Cloud instance, create a test ticket. Example: TES-1.
2. Make sure that some other user has permission to see the ticket.
3. Execute the following, in order to trigger a notification.

   curl -D- -X POST \
     --url 'https://instance.atlassian.net/rest/api/3/issue/TES-1/notify' \
     -u '<user>:<token>' \
     --header 'Accept: application/json' \
     --header 'Content-Type: application/json' \
     --data '{
     "htmlBody": "Lorem ipsum <strong>dolor</strong> sit amet, consectetur adipiscing elit. Pellentesque eget venenatis elit. Duis eu justo eget augue iaculis fermentum. Sed semper quam laoreet nisi egestas at posuere augue semper.",
     "subject": "Mail Subject",
     "textBody": "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque eget venenatis elit. Duis eu justo eget augue iaculis fermentum. Sed semper quam laoreet nisi egestas at posuere augue semper.",
     "to": {
       "users": [
         {
           "name": "<randomuser>",
           "active": true
         }
       ]
     }
   }'

Expected Results

The mail header should look like this:

From: "User who triggered the notification" <jira@instance.atlassian.net>
Reply-To: jira@instance.atlassian.net
To: randomuser@mail.com

Actual Results

From: "User who triggered the notification" <jira@instance.atlassian.net>
Reply-To: user_who_triggered_the_notification@mail.com
To: randomuser@mail.com