Why will my desktop yahoo mail not sync with my android phone app?

I have an hp laptop that I go directly to yahoo.com to retrieve my email. I also have the yahoo mail app on my lg volt phone. When I delete emails on my desktop, they delete off my phone app. But when I delete off my phone , they are still on yahoo.com on my desktop. I've tried going into my desktop to find any kind of settings I need to adjust, but am having no luck. Any suggestions?

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