Addressee and Salutation merge fields are enabled by following the steps below:

1. Log into Blackbaud NetCommunity as a user with administrative rights
2. Go to Administration --> Sites & Settings
3. Mark the Enable Addressee and Salutation Merge Fields checkbox
4. Click the Save button at the top of the page to save the changes.

The merge field will then be available for Constituent Data Sources.  
To add the merge field to the email message:

1. Go to Email > Messages
2. Click the pencil icon next to the email that you are working with
3. Select the Insert tab, and click Merge Fields
4. Expand the Bio category, and drag Primary Salutation into the message