I use an outsourced email list hosting service for a very small list, but I have been wanting to put a lot more promotion and effort into building lists on my various websites. Pricing for a small list is ok, but when I get into the numbers for potentially large lists the costs are quite significant. Through some services, that provide pricing info for this level of emails on their websites, just sending a single email to opt-in subscribers on one of my forum sites would cost in excess of $1,000. Monthly cost for unlimited emails sent to such a large list would be a bit more than $1,000 per month.
So, if I'm going to do this, I am considering to run the email system myself. That way I don't need to worry about one day having $5,000 to $10,000 monthly email list hosting bills if by some chance I succeed in growing my list into the millions (which I could probably do in a few years with the traffic on my sites). I also will soon have the excess server capacity needed to host this myself and would be able to grow with it, which would be a much better option than taking on additional costs to outsource the hosting (as money is really tight at the moment).
Managing the server, email list management software and other hosting related issues I would be able to handle myself.
What are the pros & cons of self hosting versus outsourced hosting for email lists?
What are the unforeseen issues that I might face and which I should be prepared for if I go the route of self hosting large opt-in email lists? Is there anything that ultimately makes self hosting large lists to be more expensive or significantly less effective than paying for a list hosting provider to do these things?