Although it is certainly possible to export contacts from Outlook and save it as either CSV/VCF format, this might not be the case of eml to vcf conversion, considering that .eml is just saved message. If you want to export contacts, you have to do that from the address book.
The situation is a bit different for .eml file from other software, for example Kerio Connect, which keeps contacts saved as individual .eml files on the server. Few years back quiet a few people were looking for some kind of eml to vcf converter for these, until some users came with a solution. You can read about it here, but it's not a simple file conversion.