I was somewhat dismayed to discover a few days ago that the default value of `vm-thread-using-subject' has been `t'. I had assumed that the default value was `nil' and most people weren't using this feature.
The normal method for grouping messages into threads is using their "In-Reply-To" and "References" headers. In the early days of email, these headers were not common. The standards weren't very good and many mail clients didn't bother to follow the standards that did exist. I also recall that VM's threading code wasn't up to mark in the early days. So, we had to resort to grouping messages by their subject. By version 7.19, VM's threading code was pretty good and the Internet standards also improved. It is now very rare to get messages without proper headers. (Some exceptions do exist. Typically, messages generated software - web sites or mailing list managers contain bad headers.) So, I am wondering if I should change the default value of `vm-thread-using-subject' to nil. The reason for doing this is that reference-based threads and subject-based threads conflict. Essentially, subject lines can change in the middle of threads, which means that you can't tell the subject thread of a message just by looking at its subject line. This makes VM's threading code very complicated. I think the code for reference-based threads is essentially perfect now. But subject-based threading has quite a few dark corners, some that I know about and others I don't. So, if the majority of the users don't use subject-based threads, then these problems won't affect them. So, the question is, should we change the default value of `vm-thread-using-subject' to nil? Cheers, Uday
