What is a key configuration requirement for Hybrid Message Service High Availability deployment with multiple IM and Presence clusters?
A. You must have the Intercluster Sync Agent working across your IM and Presence clusters.
B. You must have the Intercluster Lookup Service working across all of your IM and Presence clusters.
C. Your IM and Presence Service clusters must have Multiple Device Messaging disabled.
D. AXL service should be activated only on the publisher of each IM and Presence cluster.
A is correct.
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/im_presence/configAdminGuide/11_5_1/cup0_b_config-and-admin-guide-1151su5/cup0_b_imp-system-configuration-1151su5_chapter_01100.pdf