We are having issues on one of our sites that has both online forms and an online shopping cart. It's running DNN 07.03.04, Dynamic Forms 4.10.4 and Smith Cart 6.72.0. 

It started out sending all emails fine and then randomly started only sending some. There's not really a pattern as to why or when the submission notifications aren't being sent and it's happening with both the forms module and the shopping cart module.

We've spoken with both module developers and our server support team and no one can figure it out. We tried changing from emails, SMTP settings, etc. We also ran some tests with WireShark and this is what they found...

" What I can report is that the packet captures did not report any contact with our relay during either of the failures. During the successful test, I saw the login, data transfer, etc, which I would expect to see in communications with the relay. But no contact at all during the fails. What this tells me is that the issue isn't with the relay and I'm confident not with the server from a hardware/configuration perspective. However, there is likely an issue either with coding in core DNN or with the modules that are interacting with core DNN to complete the task of sending the email. "

So basically our support team has told us that it looks like something within the core code of DNN isn't functioning correctly but they aren't able to tell what.

Has anyone seen this before? Any ideas as to what's causing it or how we might be able to fix it? We have the WireShark data if that might be helpful and I have records of all we did while testing the site. Any help would be greatly appreciated!!!