@freeide - This is happening in backend or customer area? If is in customer area make sure you have enabled this option. If customer is part of group check in Backend > Customers > Group > "Group Name" > Servers > Allowed server types, if customer is not part of a group then check Allowed server types in Backend > Settings > Customers > Servers.
@freeide / @laurentiu - In most of the cases, the smtp option does not show up if your server does not meet the requirements to run it. The smtp option needs php's proc_open and popen functions enabled. Make sure your hosting is not blocking those functions, matter a fact, make sure no PHP function is blocked by your hosting company.