Hi There @gordonlangley, 

Thanks for sharing your question with us!

If you have your double opt-in turned on for your list, and you have tried to receive an opt-in message multiple tries with the same email, it might be that you are triggering an IP block. This can activate if you sign up through the same form multiple times from the same IP within a short amount of time. It’s a process that happens to prevent email blasting from a spam bot or malignant source. 

 I would recommend whitelisting our User-Agent “Klaviyo/1.0”. This documentation will walk your through the process even though it’s a Magento document the principle still applies. 

Finally, I’d check out these additional Community posts that have faced the same issue.

Thanks for participating in the Community!

-Taylor 

Hello @Taylor Tarpley - thanks for getting back to me - to be clear it’s for Admin sign-up notifications, triggered by a flow -  how do I get Klaviyo to send an opt in or re-send the opt in notifications to tom@fungimental.co.uk? - I didn’t have any issues with the other email addresses. It’s really frustrating as it’s Tom’s business and Klaviyo won’t notify him when he has a sign up from his website - Many thanks Gordon

@Taylor Tarpley - thanks again for your reply - turns out the 123reg spam filter was blocking the opt in emails. I changed my email host to ROCHEN and the email arrived immediately - I hope this helps someone. The spam filter was operating server side so my client didn’t even find the email in his Junk folder. - I think this can be marked as resolved.