Wow, what an insight.
Just FYI, the ONLY thing that changed from successful CF7 email sends to NOT WORKING, in my situation was an update of CF7 to 5.0
So this clearly means that the plugin CF7 has caused the issue.
I understand fully that every installation has its own unique parameters, any of which can affect any plugin’s performance, but when a plugin goes from working to not working after an update of just that plugin, then there is a problem – which is what these support forums are for.
Working through these issues is as time consuming for those using the plugin, as it may be for the plugin author – however, the plugin author knows exactly what they changed in the update – and therefore should have a better insight into what conflicts may be happening that the users (who in most instances are not expert coders, hence their use of the said plugin) are experiencing.
Some support would be appreciated !