Unless your blog is set up to make all links nofollow, every link you publish is automatically a dofollow link, so you have to manually change the links when necessary.
Did you read our post about dofollow and nofollow links?
While you could use a nofollow plugin, they can sometimes be buggy and cause other problems in your blog. Understanding how to build an HTML link can help you make each link nofollow by editing the HTML code in your post.
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