When someone replies to an email with an incompatible mail client eg. Blackberry, outlook express you loose your threading inside Outlook. Please:
Add a button to the toolbar “Merge into one Thread?
Also allow you to drag it into that conversation.
![Figure: Add a button “Merge into one thread?](https://bettersoftwaresuggestions.com/wp-content/uploads/2015/12/MergeThread.gif)
Figure: Add a button “Merge into one thread?