First, check your spambox. It is possible that the confirmation e-mail ended up there. Is it not there?
You may have made a typo in your e-mail address. If you are logged in (via my.guts.tickets) you can view your e-mail address at 'Your profile' and adjust if necessary. If you have changed your e-mail address, you will receive all future GUTS e-mails there.
Then, of course, you have still missed the confirmation e-mail. No panic: your ticket will not be sent by e-mail. Here is all the important information from the e-mail:
PLEASE NOTE: this e-mail is NOT your ticket
Your tickets will be kept safely online in your GUTS account, which you must open on your mobile phone. Open your tickets on your mobile phone in time to avoid long queues. You can always find your tickets on my.guts.tickets.
Install the GUTS tickets app on your phone:
The easiest way to always have your smart tickets at reach.