Gmail Tip #10: Some Tips about Conversations
Conversations are very handy. They group related emails letting you easily track what was sent and to whom it was sent.
One thing that you might overlook is that is that you need to remember that when you perform an action on a conversation such as “Print”, “Move to Trash”, or “Report as Spam”, you are affecting ALL messages in the conversation. If you want to affect only one of the messages, select or expand the message and click on the “More options” link. This will bring up a sub-menu with options specific to that message.
One other thing to note is that Conversations are not perfect. By this, I mean that sometimes (but not always), if you have unrelated emails with the same subject, they sometimes get grouped together in the same conversation. Currently, there is no way to manually “ungroup” unrelated messages. Likewise, there is currently no way to manually “group” seemingly unrelated messages into a conversation.