Hey Ryan,
What are you presently using to send out emails for your clients?
I'd agree that the software mentioned in that article is probably quite expensive, but considering the company mentioned had a list of a 1/2 million folks, I'm sure it was worth it for them.
For people like us managing smaller lists, I'd think the services of a company like Constant Contact, Aweber, Campaign Monitor or MailChimp would be helpful. Because their businesses depend on sending and delivering email for their many small business clients, I think they're better equipped to deal with deliverability issues that arise and they also have feedback loops with the major ISP's that can help them to pinpoint and resolve problems.
If you're looking to run your own software on your own servers though, I'd lookup Bailey on the forum here as she appears most knowledgeable when it comes to doing it yourself and I'm sure she'd love to share her thoughts!
Cheers,
Steve