If you wish to make your own mail server to deliver bulk mail, the main thing you have to stress is not so much the box itself it's going to be sitting on, but the stuff around it. The registrations, reverse DNS and so on.
So, the first thing you need is to get a fixed IP from your services. You can call your ISP and ask them for a fixed IP, if you do not have it currently. The second thing you have to stress over is reverse DNS lookup for your IP address, so when you do a reverse DNS lookup for your IP, you should return your business domain.
Another thing you could possibly do for your own server is install exactly what is called SPF in your DNS. SPF is generally a string in your DNS settings. And that string shows a list of all the servers that are enabled to send email on your behalf for this domain.
Some carriers, when they get email from you, would inspect if it's present. If it's not present, they might place your email in the spam folder or decline it entirely. Or offer you less points, so to speak, in the spam check. An additional thing that's optional that you could worry about is DKIM - Domain Trick Identified Mail - and you can get that if you desire however it's actually not required.
If you have a Linux box, you can go with any sort of SMTP server that's already there, like Exim or Sendmail.