If I compose and send an email and it shows in my sent folder, why would the receiver not get it?

I have a friend in Iraq, but with a yahoo mail address-


I composed and sent mail 3 times one evening and they did not receive it 3 hours after I had shown as sent--

If I compose and send an email and it shows in my sent folder, why would the receiver not get it?
They may have a spam filter on that blocks it, or they may have unintentionally blocked you, or their may be a filter on the computers internet provider that is blocking it.