You created a Nintex Workflow on your SharePoint site with a lot of ‘send notification’ actions.
What if he says that he didn’t get the email notification and that’s the reason why he didn’t take any action. (most of the times that’s the same person who has 1000 unread emails in his inbox and don’t know anything about Outlook rules and folders)
Let’s create a library ‘mail archive’ on this site and ‘mail enable’ the library with an email address. (you also need incoming mail for your lazy approval so you have to talk to your Exchange admin and Network guy anyway)
You can now send any notification mail in Nintex BCC to this list. And you can now see the exact email which is send by your Nintex workflow (and forward that one email to your nice colleague again if he asks you)
More tips in my blog post about undeliverable email