[MlMt] question about Message-ID based threading

[Peter van Dijk]

Hello,

when one of my coworkers makes a new calendar appointment, I get an 
email with headers like this:

Message-ID: 
<Appointment.c26b5086-af7a-11e8-91be-b3acf41bfd87.1535975573228 at example.com>
In-Reply-To: 
<Appointment.c26b5086-af7a-11e8-91be-b3acf41bfd87 at example.com>
References: 
<Appointment.c26b5086-af7a-11e8-91be-b3acf41bfd87 at example.com>
Subject: New appointment: ...


(I have replaced the UUID and the domain name.)

Then when somebody accepts, declines, etc., I get an email with headers 
like this:

Message-ID: 
<Appointment.c26b5086-af7a-11e8-91be-b3acf41bfd87.1535976655967 at example.com>
In-Reply-To: 
<Appointment.c26b5086-af7a-11e8-91be-b3acf41bfd87 at example.com>
References: 
<Appointment.c26b5086-af7a-11e8-91be-b3acf41bfd87 at example.com>
Subject: Appointment changed: ...



Several mail clients tie these two messages together into a thread, but 
MailMate does not. Is this configurable? Is this a bug?

To be clear, there is no actual message with the ID referred to in 
In-Reply-To and References.

Any insights would be welcome.

Thanks,
Peter van Dijk