In Motion hosting looked up the emails and none are listed.
It’s showing published. But not a single vendor says they have an email notification.
If I send to only ADMIN then I do get the email saying there is a message waiting.
If I send to Vendor & Admin then I don’t get a notification at all. Neither does our test Vendor account.
Hosting has no delay in sending. We even set up a Cron Job. Didn’t help.
Feel free to install that test plugin you mentioned.