12:32 Nov 23, 2011 

Here are the two meanings of " e-mail thread"
1. An email thread is an email message and a running list of all of the subsequent replies pertaining to the original email. The messages are most commonly organized in chronological order, and participants may refer to or re-post snippets from earlier parts of the commentary for clarification. It is customary for all participants to keep the discussion on topic, and considered poor email etiquette to deviate from the original topic.
2. The email thread as a whole is a collaborative effort with interaction among the discourse participants.

Hopefully, it helps.