By default, all emails you send from Vtiger are sent from user's email address and routed through Vtiger's email servers. Please note that you should add SPF/DKIM authentication to authorize Vtiger servers to send emails on behalf of your domain. For more details, please view this article - Authenticate your emails
To send emails from your hosting provider, you just need to setup your Mailbox in Vtiger's Inbox with 2-way sync. This can be done by each user in your CRM account.