ProxyAddress AD Attribute how to not remove existing values

Hi,

Question. I have the following configured for AD attribute “ProxyAddress”.

however, it will remove existing entry for proxyaddress and add what config to sync.

How would I set up a sync to add additional proxyaddress values and leave existing values?

this is what I have so far but it remove existing values already set in ProxyAddress attribute:

anyone can help with this?