Hi William,   Issue now resolved.  Constant Contact Tech Support told me I would need to reach out to each individual that did not receive emails.  This response was quite frankly ridiculous and I was ready to create an Event Marketing section on our website, as I know I would have no certificate issue if done through our website.  However, I really didn't want to go through the hassle of doing this.   So, in reading up in the Constant Contact DKIM and DMARC knowledge articles, I noted that my DKIM records were really different than what was used in the past, and my DMARC record did not match what was in my website DNS records.  So, I deleted the DKIM and DMARC keys in Constant Contact, got a new set of keys; entered these new key values in my website DNS records, and then reauthenticated these settings in Constant Contact.  I was informed that it could take up to 72 hours for the changes to occur.  It took about 8 hours and voila, no more certificate issues between my website certificate and what Constant Contact was referencing for my certificate.  So, the issue was either an update required from Constant Contact to match the newer way they are doing now to confirm the certificate (I have been using Constant Contact for at least 5 years and have never had a problem with certificate authentification) or somehow the reference to our certificate was hijacked.  I assume the former.   The Event URL landing page and registration page now work fine and I am all set.   I am glad I don't need to drop Constant Contact or don't have to implement the same on my website.  If this change did not work, I would have had to have dropped being a long time Constant Contact customer. ... View more