In order to import email addresses from your Mac OS address book into the Wordpress mailing list plugin, you’ll need to export them to a vCard file inside your Mac OS operating system.
Open up your Address Book application on Mac OS. Select the titles of all the addresses which you’d like to export. Then, in your Mac OS toolbar, go to “File” > “Export” > “Export vCard…”.
You will be prompted to specify a name and location for the file which will be exported. Save it to a location where you can easily find it, since you’ll need to be able to browse for it in the next step.
With your vCard file containing the selected address book contacts, go to the “Mailing List” > “Import/Export” section of the Wordpress mailing list plugin in your Wordpress dashboard. Browse to the .VCF file which has just been exported via your Address Book application. Choose the mailing list to which the subscribers should be assigned to and check the “Mac OS Address Book” radio button.
Hit the “Import” button and wait a few moments for the subscribers to be imported. All the selected Address Book contacts you exported earlier should now have been added to the specified mailing list you chose.