I received an email newsletter from Technorati, and noticed the links were redirecting through cmail1.com. I looked at the domain, and got a generic web server error message. Searching with Google led me to Campaign Monitor, a company in the business of running email marketing campaigns. Unremarkable, except that they have a really good blog covering all sorts of issues around sending HTML emails.
Now I know that this is a controversial topic, not just marketing via email, but even the existence of HTML emails. But I am often in the business of programmatically sending information in emails, and it can be a complicated business. I appreciate the care with which Campaign Monitor has shared some of their knowledge. If you find yourself scratching your head about the different ways that Gmail and Yahoo scramble your CSS (for example), you will like their blog.