Surely, if it's that difficult to send out your marketing emails, maybe people don't want to get marketing emails?
A lot of the tricky stuff is trying to make the email seem unobtrusive and make the opt-out clear so that if people don't want them, they opt-out instead of reporting spam but a lot of marketing teams still think size of audience is all important rather than quality and don't want their list size to go down by offering easy opt-outs.
Then there's the fact that a lot of people sign up for a lot of bacon, then get angry about receiving it.