Good day, @Gengus.

Can you share with me what specific error message did you get when emailing statements in QuickBooks? 

I would also appreciate it if you could add a screenshot and share the tools that you've used when fixing the error. Any additional info would be very helpful for us to ensure we're on the same page and give you the right solution. 

Please add your details to this thread and will get back to you. Have a good one.