Open Stack

On Tue, 2016-08-30 at 03:08 +0000, joehuang wrote:
> Hello, Jay,
> 
> Sorry, I don't know why my mail-agent(Microsoft Outlook Web App) did 
> not carry the thread message-id information in the reply.  I'll check 
> and avoid to create a new thread for reply in existing thread.

It's a common problem with outlook.  Microsoft created their own
threading standards for email which are adopted by no-one.  Whenever
you get these headers in your email:

Thread-topic: 
Thread-index: 

And not these:

In-reply-to:
References: 

It usually means exchange has decided the other end is a microsoft
entity and it doesn't need to use the internet standard reply types. 

Unfortunately, this isn't fixable in outlook because Exchange (the MTA)
not outlook (the MUA) does the threading.  There are some thoughts
floating around the internet on how to fix exchange; if you're lucky
and you have exchange 2003, this might fix it:

https://support.microsoft.com/en-us/kb/908027

James