Release 8.5.1.GA.3056.UBUNTU14.64 UBUNTU14_64 FOSS edition. (Single server installation)
For me this fix from article:
su - zimbra
/opt/zimbra/bin/zmprov ms `zmhostname` zimbraMemcachedBindAddress 127.0.0.1
/opt/zimbra/bin/zmprov ms `zmhostname` zimbraMemcachedClientServerList 127.0.0.1
Iptables rules works fine!
After 8 hours after turning on the firewall - it drop 61 megabyte UDP traffic to this port!
I had the same problem, and I noticed that there was a whitespace at the end of the first line. Not sure if that made a difference.
I also rebooted my sever fully, not just restarted memchaced and that did the trick.