In order to use unmanaged VPS like Vultr, you must to configure everything from install web server (apache / ngnix ) to mail server.
They are not disable anything, but if you want to use mail function, you must to config it by yourself.
What do you want to do with the Vultr.com ? If you are looking for hosting that can manage about 100,000 visitors per month with a great resources, I can suggest you a better managed hosting than these cloud services.
Linode is more a lower-end VPS provider, I wouldn't exactly consider it to be a proper cloud infrastructure as they basically just state that they are in the cloud as a marketing tactic. The whole definition of Cloud is mis-interpreted in general from what I have found with most providers. Typically for services like a VPS/Cloud I recommend the following:
vultr and linode both are unmanaged Linux VPS providers. If you are good at installing and configuring LAMP stack at your end, you can surely try them. As an alternative, if you do not want to drag yourself in server administration, you can choose VPS host who can offer VPS with pre-installed cPanel and other necessary tools.