The Bounceback you received is from one of our mail gateways. We have several mail gateways that we use to send mail for our shared and reseller servers. These boxes have a large number of IP addresses to send with and are picked at random. If you try to send your message again it will most likely route to another gateway and go through without a problem.
If you've already submitted a ticket we will apply to have the block removed. Unfortunately as there are several different organizations that setup and administer these blocks, we really have no time frame on how long until the block is removed. Really just depends on how long the administrator of the blacklist takes to do it. Fortunately since the gateways are chosen at random and switch IP's fairly regularly, this issue shouldn't plague you for more than a few minutes. If you ever see issues like this, just re-send the message. Chances are it will go through.
We apologize for any inconvenience this issue has caused and appreciate you reporting it to us.
