In article <4E319B13.8000000 at hogranch.com>, John R Pierce <pierce at hogranch.com> wrote: > 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.... References: is for Usenet news, not email. Email uses In-Reply-To. In fact, on my local server, mail messages from the centos list are fed through a filter that changes In-Reply-To to References and then fed into my local INN news server, so I can read it with a threaded news reader instead of a mail program. The group is set to be moderated, so when I post, it gets emailed to the list address. Before doing so, it goes through another filter that changes the References: header back to an In-Reply-To with the mode recent message-ID. Cheers Tony -- Tony Mountifield Work: tony at softins.co.uk - http://www.softins.co.uk Play: tony at mountifield.org - http://tony.mountifield.org