CAN ANY ONE TELL M HOW I CAN EMAIL MY FAMILY IN SYRIA THEN CAN EMAIL ME BUT I CAN'T REPLY?

I WOULD LIKE TO KEEP IN TOUCH WITH MY FAMILY IN SYRIA. I THOUGHT YAHOO WAS INTERNATIONALLY BASED. WHEN I WAS THERE I COULD ACCESS MY MAILBOX THAT I HAVE IN THE U.S. SO I DIDN'T THINK ANYTHING OF IT. NOW THAT I AM HOME THEY SEND ME EMAILS THAT I CAN'T REPLY TOO. DOES ANY ONE KNOW WHY? ANY HELP WOULD BE GREATLY APPRECIATED