I created a Nintex workflow in our SharePoint 2016 environment. It is a website workflow that runs every evening and searches a list for new items that were created on that day. The workflow then sends an email to a specific SharePoint group to inform the group members about the new list items.

However the group members do not receive the email even though the workflow notification action was successful. I talked to our exchange admin and he confirmed that the mails did not leave SharePoint; so I assume that the workflow is not working correctly.

A weird behavior is: when I tested the workflow there were only two test users in the group. While testing the emails reached the test users mailbox. Then I added the real users (about 30 users) and the workflow stopped sending the email (even if the workflow was successful). I checked every user account in our AD but they seem to be fine (no missing email-addresses etc.).

Does anybody have an explanation?