Before you can import contacts from your old mail system, you need to export them to a file. If you're moving to %BRAND_OFFICE_365_SHORT% ...

Before you can import contacts from your old mail system, you need to export them to a file. If you're moving to %BRAND_OFFICE_365_SHORT% from a webmail system such as Yahoo Mail, there is often a support page that explains how to export the contacts to a common file format such as PST or CSV. Email clients such as Thunderbird also have help files or help web pages that explain how to export contacts.