FastMail makes importing or exporting contacts simple. You can upload existing address books from vCard, CSV or LDIF files, and download your current address book in any of the same formats.
To import contacts into your FastMail address book:
vCardfile you want to import and click the Select button.
FastMail will merge imported contacts with your existing contacts, adding new entries, or replacing contact information if newer data is found in your external file. Unfortunately, FastMail does not support importing or exporting information about contact group membership.
To export your FastMail address book:
vCard 3.0, as this is the most widely supported standard.
The address book will begin downloading. Depending on your browser settings, you may be prompted for where you wish to save it on your computer, or it may be automatically downloaded to your Downloads folder.