I sent out a message today, using version 4.6.2 (should have upgraded) I have hundreds of users with PM Pro. The page went white. I got my own email, but don’t know how to tell who else got the email. Is there a log file?
There is no record kept of email sent through Email Users. If you have hundreds of users then you’ll definitely want to update to the latest version. There was a query bug I fixed specifically to handle cases where a site has many hundred (or thousands) of users.
My development site has 800+ users so I test with that many any time I make a change. I have done some work on a site that has more than 8000 users which was the source of the query changes I made a couple releases ago.
I don’t know what the upper limit is, it likely depends on the server environment.