Import email, contacts, and calendar from an Outlook .pst file

Adding and importing contacts in Proton Contacts | Proton

Import Data from other email clients to eM Client

Create a new Contact folder and enable it as an Outlook Address Book | Slipstick Systems

3 Ways to Add Email Addresses to an Address Book in Gmail, Mail, & Outlook

How to Add Contacts from Gmail, Outlook, and More to Windows 10's Address Book

How to find, add, edit, and delete your contacts in Gmail