Files with the .EML extension contain a single email stored in a single file comprised of the header of the message and its body, and possibly some attachments. This extension is used by many various email managing programs. The format was standardised in the RFC 2833 document.
After converting the file to the new format, you will be able to use other programs to support it. Keep in mind, however, that the MSB file after converting to EML may differ slightly from the original. The most important information should be kept, but if you want the file after conversion from MSB to EML to be the same, you have to do this carefully and choose the proper application from the list below.
There is no guarantee, of course, that the conversion will come up to all your expectations, but it will certainly help you. If, after all, the effect of converting MSB to EML does not meet your expectations, you can simply try to find on the Internet a different version of your file in MSB format, properly converted to a EML file by someone else. If this fails, use the information provided in the further part of the website.
Unfortunately, if after performing the two previously described steps (trying to find your MSB file converted by someone else, and the attempt to convert it to EML on your own) you still have a problem with your file, then there are only a few solutions left. You can once again try to find and install an application that can open the MSB file in its original format (without conversion to EML file). Such a solution will be difficult to implement, but it certainly will give the best result.