Report from Dropbox:
Fix the issue where emails generated about bugs that you created yourself do not have a reply-to: field that adds your comments to the maniphest task
If I create a bug and reply to the created email, it doesn’t have a reply-to that adds to the thread, so my replying to it doesn’t create a comment on the thread. In some teams, people have stopped using the email reply feature because this particular scenario makes them think the feature is flaky/unreliable.
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Make sure this isn't beyond just Maniphest too.