Clicking link in mail opens a new tab, not a new window

When clicking on a link in AppleMail, after a recent update, opens a tab in a random window or perhaps the top window in Safari. Until this update, clicking on the link used to open a new window. This is driving me nuts. I am getting links from mail opening in a new tab in Safari windows I reserve for specific topics, or uses. I do not want unrelated mail links opening and interfering with work in these existing browser windows. Also, when I see the link from mail is not wanted, I too often close the window like I usually do, but now inadvertently close a Safari window with multiple tabs of important information, that I have trouble recreating. Where did this come from!? How do I change it so a new window opens?