#Global settings
Set-ExecutionPolicy -ExecutionPolicy Bypass
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.SnapIn;

#Selects input file
$dataSource = import-csv "C:\scripts\users.csv"

#Assigns Mailbox for each AD user
ForEach($dataRecord in $datasource){
    $GeneratedUPN = "$($dataRecord.FirstInitial)$($dataRecord.LastName)@domain.com"
    $UPN = (Get-ADUser -Filter {UserPrincipalName -eq $GeneratedUPN}).UserPrincipalName
    IF($UPN){Enable-Mailbox $UserPrincipalName -Database $ExchangeDB}