HTML tags in posts

I’ve hacked admin-functions.php so that when the user makes a new post, there’s some text already there for them. Eg:

From:

To:

and so on…

I’ve done this by setting $post_content to the text.

$post_content = ‘From:<br>To:‘;

I’d like to embolden some of the lines. I’ve read in other posts that only certain tags are allowed, eg strong, em, etc. However, under certain conditions (Safari on a Mac) the tags appear literally. Is this normal?

Is there a workaround?

Cheers!