Install iOS 13.3 to Minimize Junk Messages
If you've sent a message to someone and you sometimes see an alert on your iPhone that says the message was delivered as junk, install iOS 13.3.
In a support document, Apple states that iOS 13.3 includes improvements to minimize junk messages in the Messages app that might impact certain messages that you send.
If for whatever reason you still occasionally see an alert, the company has provided a few workarounds for the issue:
If you’re trying to send a message to someone and you see an alert that says the message was delivered as junk, here are some things you can try: