As per usual both Hotmail and Yahoo have aggressive anti spam that catches normal email in its process. Unfortunately, neither provider will tell you that they've deleted these emails (they do not appear in trach or spam) and as a result you may not be aware, unless you start missing emails.
If you do, this is usually the reason why. With NZ accounts this also crosses over to xtra email and on previous forums these email addresses have been prevented from registering. However, doing this with accounts originally held from the UK may prove problematic. If you have yahoo, hotmail or xtra, and you can change you email, please do so as soon as possible.