Bulk Mailbox Script

ForEach ($mailbox in $mailbox) {Enable-Mailbox -Identity $Mailbox.Identity -Database $Mailbox.Database}

SAVE THIS AS C:\ENABLEBOX.PS1
NEXT: Run the Script
Go to Exchange Management Shell
You can change the directory to the root by typing cd\ then hit Enter (NOTE: If you just typed the words "then hit Enter" you do not belong working on servers)

Then type: ./enablebox.ps1

Just in case you want to enable archive for all users in the csv add this to the above script. 
Add <| Enable-Mailbox –Archive -ArchiveDatabase "<enter archive db name here>"}> Shown below in its entirety. 

$mailbox=import-csv C:\<filename>.CSV
ForEach ($mailbox in $mailbox) {Enable-Mailbox -Identity $Mailbox.Identity -Database $Mailbox.Database | Enable-Mailbox –Archive -ArchiveDatabase "<enter archive db name here>"}



Reference : Mailbox Script