Campaign Monitor and their companion product MailBuild http://www.mailbuild.com http://www.mailbuild.com have worked great for me. MailBuild in particular is a

Campaign Monitor and their companion product MailBuild http://www.mailbuild.com http://www.mailbuild.com have worked great for me. MailBuild in particular is a fantastic web app and I have not had any issues with delivery rates. Both products also have an API.