Clients sending email to domains hosted by Realtime are advised that messages to these domains have been backing up on our mail servers over the weekend, and are still not being delivered. A cursory analysis would seem to indicate that there is a routing problem at or near the Realtime mail servers. If you have concerns about this, please contact the intended recipients via a medium other than email and have them contact Realtime for an explanation.
Update 2010-06-15 07:26 UTC: This issue seems to be ongoing. Domains hosted by Realtime appear to be down still, and email to them continues to be queued on our mail servers.