QB also has a feature whereby if an email bounces back undeliverable, the email is put on a do not send list. No matter how many times you try to resend the invite, it will not go. If you put in a help ticket and ask them to take that email off the do not send list, it'll immediately start working.
I've run into this with new hires, IT has not set up their email account yet, but I get them set up in QB, and the system is trying to send notifications to a user who isn't ready.
Unfortunately as a realm admin, there is no published list of your domain's undeliverable email addresses to keep an eye on.
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Jeremy Myer
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