How to Stop Mac Mail from Commandeering My Preferred Email Account

For email, I prefer my Yahoo and Gmail accounts, but when I click an email address online, my Mac's Mail program automatically comes up, as if I want to use it to send my email. It also starts downloading my latest email. I frantically shut it down while trying to memorize the email address I want to send a message to using another of my accounts. I do this because when Mail downloads my email, the same new messages in my other accounts get changed from "unread" to "read." How do I stop Mail from being my default for outgoing mail when clicking on email addresses found on webpages and commandeering my incoming email?