The correct syntax for multiple email addresses (proxyAddresses attribute)
The correct way to format the proxyAddresses value when you have multiple email addresses is to separate each address with a semi-colon as shown below.
SMTP:jsmith@dovestones.com;smtp:js@dovestones.com
The uppercase SMTP denotes the primary address, the lowercase smtp denotes the secondary addresses.
Below is an example CSV file that would update existing users, create or update their mailbox.