Hi,
We have 2 CAS + HT servers set up with NLB, behind this we have 2 Mailbox servers set in a DAG. At our DR site we have 1 server with all 3 roles installed using DAC mode (also not part of the NLB cluster).
It appears that every so often, external users not running Microsoft Exchange are receiving duplicate e-mails. Checking the headers and trying to work out what is happening I think that Shadow Redundancy is kicking in and sending a duplicate from the DR site. I think one of the HT servers on the main site is using the HT at the DR site to store the backup message, it is then sending the message successfully before there is an issue with the link causing the DR site HT to think there is an issue and send the e-mail itself.
I don't have the DR site HT in the "Source" for the send connectors but the headers on the second message clearly state "Shadow Redundancy" along with the name of the DR HT.
Is there any way to stop mail routing through the DR site without disabling services? If not, is disabling services at the DR site recommended due to their being a manual failover to there anyway?
Thanks