I read your requirement and It is clear to me that you need a dedicated SMTP server and you want to send 500000 emails per days.
Relevant Skills and Experience
We have our own server farm with more than 800 dedicated servers, we are serving clients, who are sending more than millions of emails/day by our servers. All servers are protected with Firewalls.
Proposed Milestones
$220 AUD - SMTP server for 500000 emails per day.