Stamps.com said on Friday private equity firm Thoma Bravo would take the e-commerce shipping solutions provider private for about $6 billion in cash, sending its shares nearly 64% higher in premarket trading.

Stamps.com shareholders will receive $330 per share, according to the agreement, representing about 67% premium to the stock's close on Thursday.

The deal, expected to close in the third quarter of this year, is valued at about $6.6 billion including debt.

Thoma Bravo is one the largest software-focused private equity firms with more than $78 billion in assets under management. Its portfolio companies include information technology services provider SolarWinds Corp and cybersecurity firm McAfee Corp.

It has announced deals to take security software vendor Proofpoint and data solutions provider Talend private earlier this year.

Stamps.com targets its services at small businesses and home offices and helps them print U.S. Postal Service-approved postage right from their workplace. The company, which has nearly 732,000 monthly subscribers, has also partnered with Microsoft.

The deal also includes a 40-day "go-shop" period, which will allow the company to consider alternative offers, Stamps.com said.

The company's shares were trading at $324, just $6 behind the offer price.