http://Ifttt.com can do it for free 
Could set up a Zap in Zapier to do this - but more than 100 tweets per month and you'd need to pay, I believe.
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You're right! Here's the relevant applet:https://ifttt.com/applets/xcHFiVvR-get-an-email-when-there-s-a-new-tweet-from-a-specific-username …
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