Let’s be clear: Outlook 2010 is good. Very good, actually. And, certainly, if you instructed me to write an email client I’d come back to you with a white box with “INBOX” written on the front in biro.

But that doesn’t mean it hasn’t been driving me up the wall.

Outlook 2010 tries to be all clever by bundling messages into “Conversations”. This is useful for when someone in the office CC’s everyone in on which pub to go to and you spend Friday afternoon battling a deluge of witty put-downs. In Outlook 2010 everything with the subject line “Let’s go to the pub!” is rolled into one conversation and you have to scroll through your inbox less.

Problem is, Outlook 2010 isn’t particularly clever when it comes to the science bit. Instead of being smart and looking at to whom an email has been sent, it simply grabs the subject line and lumps any subsequent email with the same subject line into the same conversation. So if you forward an email from a stupid person to a clever person and add a line saying “LOOK AT THIS MORON!”, Outlook will see the subject line and make it look like you’ve accidentally CC’d the idiot. I did this last week and nearly had a heart attack.

Take this screenshot. (These emails, by the way, are different to the one which nearly gave me an aneurism last week.) Greg Salmon does PR for Microsoft Office, Tim Danton is PC Pro’s editor. It looks to the untrained eye like they’re both CC’d in on an email with the subject “Office 2010”, but they’re not. It simply means I’ve sent them separate emails which Outlook has grouped into a conversation.

Microsoft claims Outlook 2010 is more intelligent than that. A spokesman reckons “the scenario of similar or exact subject lines has been accounted for by tracking the GUID [Globally Unique Identifier] of each message,” but I really can’t see it. Take the screenshot below as an example.

Naturally, this is less of a problem if you use nice, descriptive subject lines such as “Meeting on Monday the 25th to discuss the price of tea”, but I don’t. I send messages with stupid subject lines like “I’m…” and finish the rest of the sentence in the body of the email. Or I say things like “Meeting”, and suddenly Outlook thinks I’m taking part in a giant email conversation with 98 recipients.

Microsoft is keen to point out this isn’t the final product. “We are still working on this feature, and are planning improvements to our ability to differentiate conversations with the same subject line before Office 2010 ships”, said our friendly Microsoft spokesperson.

But it’s surprising that, even at this early stage – and remember this is the Technical Preview of Office 2010, it’s not even at Beta yet – the view is so far behind other conversation-threading systems already available.

For example, Gmail offers conversation threading as well, and the technology behind it sounds similar: “Gmail threading is determined by consistency within the subject headers and references headers of email. A subject header is commonly known as the subject line and a reference header appears in the “References” line within the original, raw message information,” according to the company.

That sounds a lot like the GUID that Microsoft’s talking about it but my inboxes don’t lie: Gmail is currently threading my conversations correctly, while Outlook 2010 is very hit and miss.

You can turn it off and arrange messages simply by the “To:” field like in the old days, but I don’t want to. I like the conversation feature. I use it in Gmail all the time and it’s brilliant, and I want it to be brilliant in Outlook 2010. Certainly the rest of the application is golden: searching is nearly instantaneous in my 5,000-strong inbox and I like how a business card pops up onscreen if you hover over an email address. But until Microsoft gets the conversation feature right I’ll be treading a lot more carefully in my emails.