Hi!
I operated custom bulk senders for a long time. Getting out of spam and blacklist is a hard job. I used to use a network of smtp proxies, with load balancer to limit the amount of mail send per ip-domain name, plus, I randomly changed senders and some word in the email content.
Even with that, you need to keep an eye on blacklists (mxtoolbox is a good one), get yourself out of it when you appear.
Also, register your severs ips with google postmater and microsoft SDNS (there postmaster service)
I stopped doing it because its too much work for the little benefits...