On 07/28/11 8:52 AM, Karanbir Singh wrote: > the thing is that not all mail clients will set the in-reply-to headers, > whuch is why clients like thunderbird, evolution and mutt will use the > subject line as well to thread messages. Its the "References:" header that controls threading in mail clients that support it. I'm using thunderbird, and afaik, it won't revert to Subject based pseudo threading in the absence of References. Subject line changes don't break the thread, which is why using 'reply' and changing the subject to start a new thread makes a mess wherre the new thread is buried in the original that it was in reply to.... -- john r pierce N 37, W 122 santa cruz ca mid-left coast