Some emails never reach my hotmail inbox

First place to look is Settings > Mail > Junk email. Check the blocked senders list, and also whether the option to only trust mail from safe senders and contacts is on, that one silently bins anything from people not in your contacts. Then Settings > Mail > Rules and Sweep, you may have a sweep rule you forgot about. Also look in Archive and Deleted Items, and the Other tab if Focused Inbox is on. Ask the friends whether they got a bounce back. If nothing turns up, check Forwarding in settings, mail forwarding you didn't set is a sign someone's been in the account.