sending email to foreign country

I have a user on a old GW 5.5x system and is trying to send mail to a
recepient in Italy and gets a message DATA 554 Error: no valid recipients.
He claims to have sent this person mail in the past and it has worked. Is
there anything in the GWIA that needs to be added so mail can go to foreign
countries. I have not worked with 5.5 in a long time.