If you are looking for error-free solution to convert EML files to MSG format then I will recommend you try ZOOK EML to MSG Converter tool. The software provide easy EML to MSG migration to convert EML files to MSG format with an attachments. It is completely secure and preserves EML emails formatting during conversion process. Users can preview of EML files just before final EML to MSG conversion. It is fully supportable to Outlook 2019, 2016, 2013, 2010 and all old versions. The free trial version of the software also available for all new users.
For more info- https://www.zooksoftware.com/eml-to-msg/
To convert EML to MSG manually, you can use the following steps:
Open Microsoft Outlook.
Drag and drop the EML file into the Outlook window.
The EML file will be imported into Outlook as a new email message.
Right-click on the email message and select Save As.
In the Save As window, select Microsoft Outlook Message Format (.msg) as the file type.