Three years ago, 37signals wrote an email saying all users would have to pick new user names and passwords (I guess changing to a single sign in across all apps

Three years ago, 37signals wrote an email saying all users would have to pick new user names and passwords (I guess changing to a single sign in across all apps). It was fairly well written, but I swore it was an elaborate phishing scheme. Here is an example of one of the URLs they used: http://37signals.cmail4.com/t/y/l/uiulli/kkulljtjr/d http://37signals.cmail4.com/t/y/l/uiulli/kkulljtjr/d Now looking back, it's clear they were simply using a redirect URL to track clicks, but I had no clue. You can't even go to cmail4.com without getting an error and no description about what the service is.