If you want to migrate EML files to Outlook PST online, you can use an online converter, but it may not be suitable for every situation. Upload limits, slow processing, internet dependency, and privacy concerns can make online conversion difficult, especially when you have a large number of emails.

If you only have a few EML files, an online tool may be enough. For a large collection, an offline EML to PST converter is usually more practical because the emails remain on your computer and you do not have to upload them to a third-party server.

I always prefer to used offline tool such as WholeClear EML to PST Converter that can handle local EML files and create a PST that can be opened in Outlook easily. You can also select the required EML files instead of processing everything.

So, online conversion works for small and non-sensitive files, while offline conversion is a better fit for bulk EML files, private emails, or situations where you do not want to upload mailbox data online.