If you want to export all your users email addresses to a CSV so you can see who has which alias you can do this with this Power Shell Command
Get-Mailbox -ResultSize Unlimited |Select-Object DisplayName,ServerName,PrimarySmtpAddress, @{Name=“EmailAddresses”;Expression={$_.EmailAddresses |Where-Object {$_.PrefixString -ceq “smtp”} | ForEach-Object {$_.SmtpAddress}}} | Export-CSV c:\smtp.csv -NoTypeInformation
I have wrapped it here so just paste it in to Power Shell to run and this will show the Primary Email address and then all the alias addresses.
http://cscmblog.blogspot.pt/2012/02/export-to-csv-all-your-exchange.html