How to change the font for Elements without inline-css in an email-template for Outlook

thats the situation: I wanna create an email-template (html) as a signature that is displayed correctly in as much clients as possible. That means for example, i wanna automaticly have the text Best Regards, [my Name] at the end of any new email. But this Text should have a individual font.

The problem is: I get it to work in nearly all email clients... except Outlook. When i write an email with the template, the new text is written in automaticly generated <p>-tags. Of course, they dont have any other arguments, like inline-css.

And these parts of the email are not changed by my style-tag in the template part (in outlook. A browser or other email clients, give this p-tags also the new font).

E.g. : the template for my signature is

<p>Best regards</p>
    <p>John Smith</p>

    <style type="text/css">
      *,p {
         font-family: "calibri";
      }
    </style>

Then Outlook changes the font of the text "Best Regards, John Smith" to calibri, as intendet. But when i type some text into the email, like "Hello Resiever, this is my message", then this p-tag doesnt get the new style in Outlook and is displayed in the default Times New Roman. Even when i checked in my thunderbird-email before sending, that all the text has the font calibri.

Here are some more infos:

• Yes, the self written text (e.g. "Hello Resiever, this is my message") is in a p-tag. I checked it in the email-source code
• Until now, this only happens to me in outlook
• in my original template, i use inline-css for my tags. But this is no option here, because the p-tags of the email-content are generated automaticly
• Yes, i already googled it. But i didnt found any working solution
• I cant just change the default font, because i want this email to display correctly on other computer too (that should be obvious ;) )
• It should work for the current version of outlook

I really hope, there is someone out there, who can help me with this problem. If you need any more, or more specific information, just tell me :) Thanks for all answers and to all the people, that at least try to help!