[Mailman-Developers] How to check whether the message is new thread!

[Stephen J. Turnbull]

VuNghia Truong writes:

 > Could any one please give me advices about how to check if a message is a
 > new thread or just a reply to a thread?

Check for a References: header or an In-Reply-To: header.  These
headers contain message ids from the thread.  If they aren't present,
the message starts a new thread.

Technically, the presence of these headers *defines* "thread".  In
practice, you may also want to group messages with the same subject in
the thread.  However, there is no good way to determine order without
the References or In-Reply-To header, so for most lists it is not
worth the extra effort to analyze two headers to see if they're really
the same after stripping out various prefixes and affixes added by
software along the way.

Steve