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I checked your following form: http://www.jotformpro.com/form/51354683383965, and two of the recipients were in bounce list: https://www.jotform.com/help/262-How-to-Remove-Your-Email-Address-from-Bounce-List
They have now been white-listed, so this should solve the problem. In addition to this, I would recommend you to white-list our IP addresses and domain names(or ask your email provider to do it), in order to prevent this from happening again: https://www.jotform.com/help/145-Whitelisting-JotMails-IP-Addresses
If there is another form where notifications are not being delivered, please let us know, we will be glad to assist you.