Failure Notice Does Not Like Recipient - 550 Bad CT IP Reputation

If you get an email bounce back with the error "failure notice does not like recipient" then it's an easy one.

It means that the email server of the company of the person you are trying to reach has rejected your email based simply on your sending email address (more correctly, the IP address).

Most big companies use some kind of reputation checking service. For example, Mimecast is one of the huge ones (in fact, Mimecast is a much bigger overall email solution). There are others too and just like credit checking companies, there are a handful of big global hitters when it comes to reputation checking.

If you get this message then it is usually a problem with your sending IP address. There may even be a further message such as "550 Bad CT IP Reputation". In this case, the "CT" actually refers to the blacklisting company, CommTouch.

You need to visit the big reputation keepers, check your reputation and, where bad, raise a request to be white-listed.

Some of the major ones are Commtouch, Mimecast, Spamhaus, AOL and others. You can find larger lists of them online. Here's one such blog post containing the big hitters. If your company cannot send email to external clients then you need to go to all the reputation checkers and tell them to whitelist your IP address.

We had this problem ourselves when we changed our company internet connection. The new IP we received just happened to be on a blacklist!