eM Client can import your data directly from Microsoft Outlook, Thunderbird, other popular clients, previous eM Client database or relevant data files.

When you first run the application, an automatic import wizard will lead you through the process if it detects that you have other email client(s) installed.

Besides this, the import options can be accessed at any time in Menu > File > Import.
This option allows you to import your emails from .eml files, contacts from .vcf or .csv files, calendar and tasks from .ics files or even eM Client settings from .xml files.

Read more in our blog: Import Data from other email clients to eM Client and in the Documentation: Getting Started.