PayPal Instant payment notification warning

We received the following email from PayPal several times. We have noticed that it occurs after someone submits a payment via one of our Jotforms. 

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Hello Billy Vaughn ,

Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) are failing:

http://dtui.us9.list-manage1.com/subscribe/paypal-ipn?u=9b533206ab2971d01792fd15b&id=d1053b9867

If you do not recognize this URL, you may be using a service provider that is using IPN on your behalf. Please contact your service provider with the above information. If this problem continues, IPNs may be disabled for your account.

Thank you for your prompt attention to this issue.

Thanks,

PayPal

PROTECT YOUR PASSWORD

NEVER give your password to anyone, including PayPal employees. Protect yourself against fraudulent websites by opening a new web browser (e.g. Internet Explorer or Firefox) and typing in the PayPal URL every time you log in to your account.

Please do not reply to this email. To get in touch, go to the PayPal website and click "
Help & Contact
https://www.paypal.com/selfhelp/home ".

Copyright © 1999-2016 PayPal. All rights reserved.

PayPal PPX000686:63255ba3517ca

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Please advise.

username: dtuiadmin

Thanks ahead.

Billy Vaughn

That message is most likely not related to the JotForm service. The IPN URL seems to be related to the MailChimp, so I would like to suggest contacting them to investigate this further.

If you need any further assistance, please let us know.