Gmail新功能 - Google

Reply by chat
Just what it sounds like… when you're about to (or in the middle of a) reply
to someone, and you see that person online, you can just send your reply as a
chat message. And if you've chosen to save your chat histories, then your
chat even gets threaded with that original email conversation.

好像不算什麼強大的新功能

就是回信的時候可以選擇直接跟對方聊天

http://mail.google.com/support/bin/answer.py?answer=34539&hl=en

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