There seem to be some people in the big world of blogging that have posted that the correct way to get Outlook messages to be correctly crawled and made searchable within Sharepoint is to edit the registry.
They are now out of date, as Microsoft have released a Filter Pack that provides this functionality, albeit undocumented.
The 3 blogs I have found are as follows :
If you follow their advise you will firstly be taking a risk by altering your registry (always back it up before making any changes) and secondly creating a solution that does not work fully. I tried all 3 of the slightly altered solutions, none of which were able to produce the results I required, which was to index & search .doc attachments, worked ok for .docx. Also it is worth noting that it did not prefix the summary/extract with the attachment's filename, so the context of the result was lost.
Now the most recent method it is to install Microsoft's Filter Pack which provides all the correct iFilters for Microsoft Search products to use; including Sharepoint. I performed a restart of the server after installation and then a full crawl and it produces very nice results for all the emails and attachments that I need.
I recommend that you don't fiddle with the registry unless there is no other way, admittedly this is not documented anywhere and it was more by luck that I discovered this than anything else. So credit to Gavin, Tom and Lirliron for what they discovered, but a much more complete & safe solution is to download the filter pack from Microsoft, the link again is here.
Also, just so that you are aware, if you already have the PDF iFilter installed and expect this to mean that you can index and search pdf attachments, you will be disappointed as it does not work.