Have a look at this,http://www.cisco.com/c/en/us/support/docs/unified-communications/unified-communications-manager-callmanager/117726-technote-cucm-00.html

Do you still face this issue?You can open a TAC case for assistance. Will need to look at Conversation manager and MTA logs.

Sorry for the late response. Got held up and couldn't look into this. The best way is to set Message Aging Policy. If you need to Bulk delete the old messages, you can open a TAC case and ask the engineer to help you delete the messages. You can ask ...

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