In order to send bulk messages to relationships based on their assigned tags, you can follow these steps:

1. Access the gear icon located at the top right corner of the interface.

2. Select the "Tags" option from the menu.

3. Choose the desired tag from the list by clicking on it.

4. Tap on the three-dot icon situated at the top right corner.

5. From the available options, select "Email to all (bcc)."

By following these steps, you will be able to efficiently send bulk messages to recipients associated with a specific tag.