A lot of email is 'reputation based', this come from a combination of both the IPs and the domains being sent from. A good practice is to 'warm up' the IPs and domains by sending a good amount of non-transactional emails to start with that your lists will find appealing. Don't send generic content, but rather send good quality content that users read. It's also a good practice if you can create content that is appealing for the user to forward, this scores strongly with ISPs.
Remember, the ISPs have teams and resources committed 24/7 to putting emails in the right place- inbox, promotions, junk or blocked. Create your reputation to be desirable. This will serve multiple benefits; 1) Better deliverability; 2) Better engagement with your user base; 3) when you do send transactional emails, you will have a higher trust level, leading to increase open rates, conversion rates etc