Use below power shell in exchange shell to create a mailbox and account at the same time
New-Mailbox -Name “Prem Rana” -Alias “premr” -OrganizationalUnit “hitechcandy.com/People”
-Database “mbxDatabase1” -UserPrincipalName premr@hitechcandy.com -SamAccountName “shanek” -FirstName “Prem”
-Initials “P” -LastName “Rana” -ResetPasswordOnNextLogon $true