EML files are how Windows computers save or export emails. There are lots of uses for these, from backing up private email locally to transferring data from one email service to another. Microsoft Outlook organises email files into PST, personal storage tables, which isn’t immediately compatible with EML.
Thanks to EML to PST Converter, this is no longer an issue. You can have a free trial of this software which isn’t pretty but it works lighting fast and lets you convert the emails in bulk, plus your attachments are kept intact.