Outlook uses a different way of executing stylesheet. Is not SMTP settings or email settings. It depends on how the email service like Gmail, Outlook and Yahoo displays the CSS. How Outlook styles = How IE styles.
I've used Mailchimp did this for every p
element I used and it does not looks exactly the same in Outlook and Gmail but is the closest I can get.
The guide I used for Outlook is this. Do note that you have to join their community ( free) to get the Outlook guide, which I think is worth it and save you the trouble. https://www.emailonacid.com/resources
The previous link should explain to you but if you want more information, you can always look the below two links that I used as well.
For Outlook/Hotmail, they usually have a mso
syntax in front of the styling like
http://templates.mailchimp.com/development/css/outlook-conditional-css/
For certain elements that email provider use, you can refer here. https://www.campaignmonitor.com/css/
Spend some time creating a email template that works for all email services and modify it next time to suit your needs saves much more time and effort than starting from scratch.