Wanting synchronization capabilities and frustrated with a bizarre folder locking bug - a folder remains locked if a connection is dropped server-side while downloading mail - which I was too lazy to fix, I switched from Thunderbird back to Outlook 2003. It's actually a lot better than I remembered (having worked with it extensively from a development point of view until last year); when not working against an Exchange server (and on a gargantuan Athlon 64-based machine) it's actually very fast, doesn't stall and is pretty stable at that.

It's not, all in all, a bad product. But it's not a complete one either.

First and foremost, Outlook's search capabilities are so ridiculously bad that third party tools have been coming out for years to address this shortcoming. Among those are Google Desktop Search, MSN Search Toolbar beta, Copernic Desktop Search and very much my personal favourite, Lookout. Lookout is an Outlook plugin written in .NET (one of the first commercial-grade products I've ever seen to use the platform) which indexes your mail in the background and performs extremely fast searches. It's complete free and was, in fact, so good Microsoft bought the company a couple years ago and is presumably busy incorporating Lookout's features into Outlook 12.

Second, the spam filtering options are lacking. I've no idea what sort of mechanism Outlook uses, and it is effective for certain kinds of spam, but it also generates a lot of false positives and misses a lot of other spam. Looking for a client-side (i.e. non-proxy) bayesian filter implementation for Outlook I eventually settled on SpamBayes, which is so far completely stable and hassle-free - not to mention effective, and open-source at that.

Moving back from Thunderbird was not without hassle though; I wasn't inclined to import the Thunderbird mails over to Outlook so that wasn't much of an issue, but I couldn't get the "Send To Mail Recipient" shell option to work with Outlook. Theroetically, merely changing the default mail program in "Internet Options->Programs" to Outlook should do the trick, but it appears not to be the case. I eventually found a solution on Joel's old forums: start RegEdit, go to HKCU\Software\Clients\Mail and change the default value from "Mozilla Thunderbird" to "Outlook". That's all there is to it.

As a bottom line, if you do not require simple bidirectional mail support or PDA synchronization via ActiveSync, stick to Thunderbird. It's a basically superiour piece of software.