
In a new support document, Apple has indicated that iOS 13.3 includes improvements to further minimize junk messages in the Messages app.

If you are trying to send a message to someone and you see an alert on your device that says the message was delivered as junk, Apple has provided some potential solutions to get around that:
iOS 13.3 was publicly released earlier today.- Ask the person that you're trying to message to add your phone number to their Contacts.
- Ask the person that you're trying to message to send you a message to start the conversation.
- On your device, go to Settings > Messages > Send & Receive and make sure that only your phone number is selected under Start New Conversations From. If your Apple ID is selected, the messages will be delivered as junk.
- If you're on an iPad or iPod touch, turn on Text Message Forwarding from your iPhone.
Article Link: iOS 13.3 Includes Improvements to Minimize Junk Messages