My point was transactional emails does not hit any spam filters. And since email services tracks how many of emails were opened, i am pretty sure 'we have been hacked' will be opened quite often and will never be in spam folder.
From the point of view of a spam filter, there isn't really any difference between a "transactional" (what a horrible name, but not your fault that the industry has adopted it) email and any other email.
"Transactional" emails simply have some distinctive elements, such as the first and last name of the customer, which make them less likely to be filtered out.
First & last name in email alone doesn't guarantee to hit inbox. Huge free email services use social 'signals' as open rates, 'this is spam', 'this is not spam' as well as IP reputation i mentioned earlier to determinate if email hit inbox.
So, there is obviously a difference in those metrics between simple notification 'your account have been hacked. change password' and 'hey, we haven't seen you for ages'. As email system notice high user involvement it will never ever block such emails. Actually, i think it will increase IP reputation.
"transactional emails" is a term marketers use, but in reality the email systems do not know the difference. And yes we did get stopped by various ISPs, and yes we did have to get some on the phone.
