Echoing what a lot have already said. I worked for a large email marketing provider that was acquired by Salesforce about a decade ago. The number one thing y

Echoing what a lot have already said. I worked for a large email marketing provider that was acquired by Salesforce about a decade ago. The number one thing you are selling is deliverability. The second thing you are selling is the tracking (opens, bounces, unsubscribes, etc.). Next, you are selling segmentation for subscriber lists (i.e being able to send the right message to the right consumer at the right time). You have to be diligent about your customers too, because if you are letting bad actors use your system... there goes your reputation and there goes your business. But deliverability is the key. We had relationships with ISPs so we could fix $MAJOR_CORP's million email pre-holiday sales campaign while it was sending and we staffed the teams to do that, 24/7. This had nothing to do with programming and everything to do with company mission, reputation, contacts at Google, MSN, Yahoo, ..., and the history of having done it. We were "lucky" enough to have started as the industry matured. * I say "lucky" because the founder's really caught this vision at the right time (2000/2001) and made it happen.