Well last time I had to fuck around was because the entire IP ranged ended up on an RBL and I couldn't deliver to half the people I needed to. Oh and then there

Well last time I had to fuck around was because the entire IP ranged ended up on an RBL and I couldn't deliver to half the people I needed to. Oh and then there was that time that Yahoo did its thing and asks you to fill in a web form to continue delivering to them, the URL of which is neatly hidden in an SMTP response message. If you get that form wrong or they don't like the answers they will just ignore you for 6 months.