Some email internet providers can mark general booking emails such as those sent from Viator as "spam" - please check your spam folder for previous email replies. If you have your spam filter set on the highest ranking, only emails from senders in your address box will go into your inbox. Any other emails (such as replies from internet sites you have booked on) will go into a "spam" folder. These emails can sit in this folder for up to 7 days and then your email system will automatically delete them.