NEW YORK ( TheStreet) -- Stamps.com (Nasdaq: STMP) is trading at unusually high volume Monday with 559,950 shares changing hands. It is currently at four times its average daily volume and trading up $1.72 (+8.8%) at $21.16 as of 3:55 p.m. ET. Stamps.com has a market cap of $265.3 million and is part of the services sector and retail industry. Shares are up 46.7% year to date as of the close of trading on Friday. Stamps.com Inc. provides Internet-based postage solutions. The company has a P/E ratio of 25.1, above the average retail industry P/E ratio of 24.8 and above the S&P 500 P/E ratio of 17.7. TheStreet Ratings rates Stamps.com as a buy. The company's strengths can be seen in multiple areas, such as its largely solid financial position with reasonable debt levels by most measures, notable return on equity, attractive valuation levels, solid stock price performance and compelling growth in net income. Although the company may harbor some minor weaknesses, we feel they are unlikely to have a significant impact on results. You can view the full Stamps.com Ratings Report. See all heavy volume stocks in our stocks moving on unusual volume list or get investment ideas from our investment research center. Interested in other stocks that are rising on unusually high volume? Get free SMS text alerts sent to you when the action happens by texting HVUP to 95370 or select from multiple alert options.