How to ensure emails are sent only once to users in a Views Block Operations (VBO) list?
You can adapt my answer with a "trick filed" on your content type in this (last) answer. Update "trick field" when your mail is sent the first time.
Why is my rule that reacts on event &quot;After updating an existing user account&quot; firing twice?
Then hide "trick field" modifying your "form-id" and field name with this solution (2nd answer) Is there a way to prevent a user from seeing a field on their user profile page?