My iPhone is blocking texts from sources that should not be blocked. There is not "this is not junk" option

Go to Settings>Messages>Message Filtering>Unknown & Spam. Do you have any apps checked under "SMS Filtering"? If so, disable them. If that doesn't help, this may be a carrier issue.

The message that says "The sender is not in your contact list. Report Junk" could mean that the message was sent using their Apple ID email and you do not have that information listed in your contacts. Using iMessage, the message can be sent with either their phone number or email.

If they do not respond to the message and are using iMessage with the blue bubble, when you reply. It could be a setting on their phone. They can choose to send messages using either their phone number or Apple ID email and also choose to receive messages from their phone number or Apple ID email or both. They should check that both options to receive messages is set at Settings > Messages > Send & Receive.

If it’s blocking them, how do you know?

What are you seeing and why do you think they are “blocked”?