eM Client supports export to all standard file types for all your items.

You can export emails into an email message format (.eml), calendars and tasks into iCalendar files (.ics) or your contacts into VCards (.vcf).

You can also export your account settings, rules, signatures, and other settings into a .xml file and import it into another instance of eM Client.

The export feature is accessible in Menu > File > Export.

Read more in the Documentation: Export