Nope, however if you create and pin a banner topic every X days or weeks, any users that access the site in that time frame will see it, any user who does not visit the site in that time frame will see the topic in the summary email (if the user has the summary emails enabled).
In your case, if you want to send all the users the same email without distinction, you should use the newsletters. You could export all users in bulk from Discourse to extract their emails and use them to send regular newsletters to everyone.