Text Extractors - if nothing else the text from a corrupt mail file can be extracted. You may be able to reconstruct your messages at that point.
Please note: Honestly the commercial software and services is the route you will sometimes have to take to recover your data. Generally, it's a lot easier to find free programs for file repair for non-Microsoft products than Microsoft ones. You can explore them by following the links to the left.
On those occasions that you try the freeware and it doesn't work, the software in these pages will appear not be worth the time and effort you put in and this can be frustrating. I try to point out at the top of each page, what I see is the likelihood that and difficulty with which freeware can recover your data.
The Google Adsense Ads displayed on the pages should lead you to the standard commercial software and services available for the problem you are having. You can also try the commercial links by clicking on the Navigation Bar by the file type name on the left. It's also here.
To see if the program works before buying, always be sure to try the demos of commercial software first. Also the difference in prices for software that does the same thing, for instance recovering PowerPoint Presentations, can be a large range like with PowerPoint case $50 - 299. If possible, try several software solutions before buying. For services, be sure there is a no data, no fee guarantee, and a recovered file preview available.
If you need help, I charge $22 per incident. You can E-mail me at firstname.lastname@example.org, but because of finances and legalities, I only use free methods.