Send me a PM with yor contact info and we can sort it out. Most likely its some sort of spam filter or DNS resolution issue. Quick things to try would be to clear you mailservers DNS cache. We had made a few changes to our mailing DNS setup, and some mailservers hold longer caches then what they should to try and keep DNS lookups down. If you have any copies of log files of the failures that would be great, or if we can setupa time where I can shuffle out some test messages to you that would also help to figure out whats going on.