[TxMt] Re: Mail threads on this list keep breaking

[Allan Odgaard]

On 27 Mar 2013, at 15:24, Berend Hasselman wrote:

> It would be really nice if it can be fixed on the list side, assuming 
> it has something to do with the message headers or?

Agree, but I am clueless as to what can cause this.

The correct headers are clearly there, as other clients have no issue 
threading the discussions (even previous versions of Apple’s 
Mail.app).

Given that only this list is known to be affected, there must be 
something different, but how would I debug this?