[kitchen]

thunderbird does do subject-based threading by default. Fortunately there's a way to disable this by enabling strict-threading.

Threading works by using the In-Reply-To: and References: headers in emails. This way you have a direct correlation between an email and what it was replying to. It allows you to trivially build a tree structure for a thread, which is what a thread is, not a flat conversation.

I get lots of emails from our notification systems that have similar or often the same subject. Having it thread by subject alone is extremely irritating here because it combines completely unrelated things together.

[sp4rki]

Ahh I understand. I generally don't use threading (I rather threat emails as a standalone items), but I can see why you'd find subject threading annoying. I tend to filter emails and reroute different types of emails that don't belong in my inbox to other systems, so I don't see a need to be as stringent on the requirements for threading. That being said, I don't know if any clients that would fulfill your expectations. I guess you're stuck with Thunderbird!