[yanchuk]

hey. notice: i work for mailtrap.io but I have domain knowledge

It's always better to separate your transactional and bulk (marketing traffic). We do it as well as it's also best practices recommended by Gmail (use different IPs, and even subdomains). Also another thing is suppression list: as somebody marks you bulk email as Spam, they still can receive their e.g. pass reset emails.

It's probably nothing cheaper than SES, but you probably need more time with it. And if you have any issues with deliverability - you are on your own. Postmark or we provide support, UI, etc for extra costs.