Notifications: New subscriber email lands in spam

A [customer reported](https://app.plain.com/workspace/w_01JE9TRRX9KT61D8P2CH77XDQM/thread/th_01K224Y7M1RQM4JK7HAREFGTBH/) that the email for new subscriber landed in spam for them as following:

<img width="1710" height="738" alt="Image" src="https://github.com/user-attachments/assets/e8da21d6-7a7b-442d-bf6d-2e28c6eecad5" />