Hello everyone, thanks for keeping us posted on your results here. We're not seeing the same looping behavior during testing, so I suggest submitting a support ticket so we can take a closer look at this. One thing that works after you've upgraded to 7164 is to add an SMTP Block under Settings>Security>SMTP Blocks for the offending from addresses, then remove the already existing messages in the spool. Once cleared out you should be able to remove the SMTP Block and resume normal operation. Please give that a shot and reach out to support if these issues persist. Thanks!
Kyle Kerst
IT Coordinator
SmarterTools Inc.
www.smartertools.com