Q: What exactly happens when you block a person on your iphone?

Lex, here is what happens:

They are not notified that you blocked them. If you want them to know, you would have to tell them. Blocking prevents delivery of the message. Undelivered blocked messages are not stored for later delivery. Unblocking resumes delivery of that person's new messages. Calls roll directly to voicemail. You can navigate to listen to them or not as you choose. If you send them a message they should receive it as blocking is one directional. More details here:

Block calls and block or filter messages on your iPhone, iPad, or iPod touch - Apple Support

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