The correct syntax for multiple proxyAddresses
The correct way to format the proxyAddresses value when you have multiple addresses is to separate each address with a semi-colon, the address can be enclosed in quotation marks if necessary but this is not essential.
”SMTP:user@domain.com;smtp:user2@hotmail.com”
Notes:
- The uppercase SMTP denotes the primary address.
- A lowercase smtp denotes the secondary addresses.
- There is no way to guarantee the order that the addresses are displayed when viewed in AD Users & Computers.