Stamps.com (STMP, $323.74) agrees to be acquired for $6.6 billion

Internet-based mailing and shipping services Stamps.com  shares rose on Friday, after the company agreed to be acquired by private-equity firm Thoma Bravo for $6.6 billion .

Under the terms of the deal, Thoma Bravo will pay $330 cash for each Stamps.com share. That implies a +67% premium over the stock's closing price of $197.72. on Thursday. The deal could close the deal in this quarter, subject to conditions including regulatory approvals and a vote of Stamps.com holders.

However, the deal includes a 40-day period (through Aug. 18) during which Stamps.com  can actively seek better acquisition proposals. During this period, the board will have the right to terminate the Thoma Bravo agreement without penalty.

Chief Executive Ken McBride said that with Thoma Bravo's backing, Stamps.com will intend to capture the expanding e-commerce shipping market.

"The e-commerce landscape is rapidly evolving and we look forward to partnering with the Stamps.com team to continue building on the company’s leading position in e-commerce shipping solutions," said Thoma Bravo principal Brian Jaffee.