Constituent Attributes can be added to messages using the data source of Constituents. 
Note: if you want to use other types of attributes than Constituent, you must set up custom merge fields for email messages

To add constituent attributes to your email message:
  1. Ensure the Constituent attribute is created in The Raiser's Edge - this only needs to be completed if the Constituent Attribute is not created in Raiser's Edge yet
  2. Make the Constituent attributes from The Raisers Edge available to Blackbaud NetCommunity
  3. Insert the merge field into your mailing:
    1. While editing the email message in question, navigate to Insert>Merge Fields
    2. Expand Constituent Attributes
    3. Double click or drag/drop the desired attributes
    4. When finished, click Save
Additional resources:
How to add new merge fields or attributes to acknowledgement emails, eReceipts or Notification emails