Outlook only provides direct support for importing addresses from Outlook Express or Eudora. However, it does allow one to import addresses from a comma-separated (.csv) text file. If your current mail client will allow you to export the address book as a .csv file, you should be able to import the addresses into Outlook.

1. Save or export your current address book as a comma-separated (.csv) file.
2. Within Outlook, go to the File menu and select Import and Export.
3. Choose "Import from another program or file" and click Next.
4. Choose "Comma-separated values (Windows)" and click Next.
5. In the "File To Import" box, browse to the file to be imported and click Next.
6. Click to select the folder you want to import the records into, and click Next.
7. Click to select, Import "<FILENAME>" into the "<Folder name>" folder.
8. In the "Map Custom Fields" dialog box, click each field name in the From window that you wish to import and drag it to the corresponding target field in the "To" window, click OK, and then click Finish.