Currently, if you someone in a message they are added as a recipient. If you delete that the person is still listed as a recipient and you must manually delete them from the field as well. In practice, this proves problematic because some users either expect the recipient (which was automatically added to the field) to be automatically removed from the field when the is deleted. Other users might just forget to remove the user from the field.

We could be more intelligent about this. We could track recipients added automatically vs recipients added manually. If we automatically added a recipient, they might show up in the field using a slightly transparent recipient chip (or some other UI indicator). Hovering over this recipient chip would show a tooltip informing you that they are automatically included as a recipient because they’ve been mentioned in the message below. At this point, if you deleted all mentions of that recipient they’d automatically be removed from the field as well. However, if you manually add this person as a recipient to the field, then they’ll show up with a fully opaque recipient chip. Now, if you also mention them and then delete that mention they won’t be deleted from the recipient field. Similarly, if you mention someone in a message, automatically adding them as a slightly transparent recipient in the field, then you could still manually add them as a recipient in the field. If you did so, then instead of adding another recipient chip the existing recipient chip would just become fully opaque. If you attempted to delete this recipient chip, rather than being removed it would become slightly transparent again (at this point, deleting all of this person from the message would automatically remove their recipient chip).

This might sound like a long explanation, but in practice I think it **** be an rather intuitive user experience.