Appending to a list of proxyAddresses in Exchange Management Shell

Adding to a list of EmailAddresses in Exchange has the potential to be one of those 'gotcha' issues that, if performed incorrectly, can really make you momentarily rethink your career in IT.  This is because if proper measures are not taken, the list of mailbox alias' can be overwritten by your one addition.  For example, if the following command was run, all pre-existing proxyAddresses would be overwritten with the addition of userA1@domain.com:
 

Set-Mailbox userA -EmailAddresses 'userA1@domain.com'
                      

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The process to work around this has traditionally involved adding the complete list of alias' each time instead of just the one like so:
 

$user = Get-Mailbox userA
                      $user.EmailAddresses += 'userA1@domain.com'
                      $user | Set-Mailbox
                      

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A simple work around available in PowerShell 2.0 and beyond involves the use of an array:
 

Set-Mailbox userA -EmailAddresses @{add='userA1@domain.com'}
                      

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Now we can add just one address at a time instead of being forced to account for the entire list with each new request.  Enjoy!