In Gmail, all email responses are grouped with their original message, creating a single conversation or thread. This is different from Outlook and ArgoMail where responses to an email message each appear as separate items in the Inbox. You can identify Gmail conversations by the number next to the sender's name. In the example below, the number indicates that this is a conversation that contains 5 messages. The bold name indicates that there is a new message from that person (in this case, Nona).
When you open a conversation in Gmail, all of the related messages are stacked on top of each other with the newest on the bottom. Messages are always displayed in chronological order. Messages that you previously read are collapsed (unless they have a star), and new messages are expanded. When you open a conversation, scroll down and start reading at the first expanded message - that's where you left off.
To expand a collapsed message, click on the sender's name. To expand all the messages in a conversation click Expand all.
Gmail offers the ability to switch between conversation view and the traditional message-based unthreaded view. If you switch to unthreaded view, messages are no longer grouped together into conversations, and each message is shown as a separate entry in the inbox. To turn off conversation view, open Settings from the upper-right corner of Gmail. Then, go to the new Conversation View section, change the setting to Conversation view off, and click Save changes.
Mobile Devices: The mobile web-based view of Gmail will still be threaded, as will the Gmail Mobile Client app. However, if you are using a Blackberry, Windows Mobile, iPhone, or Android device, you can access Gmail unthreaded in the native mail clients of those devices using Google's sync tools.
Gmail groups messages into conversations based on their subject line. So, if you get three messages titled "Project," they may be grouped into a single conversation even if the messages are about three entirely different projects. To avoid this, use more specific subject lines.
If you are responding to an email message and do not want the response grouped with the original message, change the subject line in your response. Click the Edit Subject link in the blue section above your response.
Labels must be applied to an entire conversation.
You can't label a specific message in a conversation. The best alternative is to label the entire conversation, but also apply a star to the specific message that you're interested in. In the future when you open the conversation, the starred message will be automatically expanded for easy reference.
Conversations can be archived just like single messages; however, if you receive another response to the conversation, the entire conversation will be returned to the Inbox.
To forward an entire conversation, open the conversation then click Forward all on the right. This will open a new message that contains the entire forwarded conversation. Before sending the forward you can delete any information that you do not want to include in the forward.
To forward a single message or just a portion of the conversation, expand the most current message that you want to include in the forward, and then click the Forward link that appears below the message. In the forward, Gmail will include all messages that were sent earlier in the conversation, but just like "Forward all," you have the opportunity to delete any information that you don't want to forward.