Environment
GWAVA 4.5 and Newer
Situation
DNS lookups are taking too long (timing out) causing some senders to resend their message, which will cause duplicate messages.
Resolution
If you are receiving duplicate messages and have found in the GWAVA logs that the DNS lookups (done on RBL and SURBL events) are taking too long or timing out after 10 seconds, then your server may be using mDNS. mDNS is a service that tries every machine on your network looking for dns info. It is recommended that you turn this off. You can do this by:
1) Using Putty type: vi /etc/host.conf (this will open the host.conf file).DNS lookups should be faster now, allowing mail to flow faster which in turn will prevent duplicates from happening.
2) Hit the 'Insert' key, this allows you to edit the file.
3) At the bottom of the file type: mdns off
4) Hit the 'Escape" key
5) Type: wq (this will write the changes to the file and quit the file)
6) Reboot the server, type: shutdown -r 0
Additional Information
This article was originally published in the GWAVA knowledgebase as article ID 2032.