i know of deployments that had something like 50K and were working fine, the main concern would only be the time it takes to sync between the CUCM and the AD.
if they deleted an user it could take up to 3-4 days for it to disappear from CUCM
they also had high performance servers to support this, not sure what servers you have
HTH
java
if this helps, please rate
HTH
java
if this helps, please rate
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