Over the past week, several startups have received e-mailed pitches from IBM(IBM), offering patents for sale in their areas of expertise. That raised eyebrows among the recipient companies, who said the cold-calling aspect of the pitches was out of the ordinary for IBM, although it is not at all unusual for any large patent holder to sell off patents that are not key to its businesses.
One reason is that patent holders have to pay maintenance fees on patents several times over their 20-year lifetimes. That can add up, especially if the company is holding on to thousands of patents it doesn’t plan to utilize.
In one letter, IBM offered an array of data analytics patents at $37,000 per patent. The recipient could buy the entire list or any part of it but IBM asked to be alerted as to any interest by August 28, so transactions could be closed by September 18. For what it’s worth, IBM’s third fiscal quarter ends September 30.
And IBM is indeed patent rich. It has been the leading patent holder in the U.S. for more than 20 years, by a significant margin. In 2014, for example, IBM was number one with 7,481 patents granted. Samsung Electronics was second with 4,936. IBM patents have shown up in applications far and wide, including in LASIK (or laser-assisted in-situ keratomileusis) vision improvement procedures.
Patent grants are a point of pride for tech companies including Apple(AAPL), Intel(INTC), Microsoft(MSFT) and Google(GOOG), who point to their patents as proof of their ability to innovate. Maintaining those huge portfolios can get pricey.
Still, according to a veteran venture capitalist, a Boston-area patent attorney, and a CEO who got a letter, the cold call tactic was unusual. Vendors are more likely to post available patents on a web site, they said. IBM has one.
Said the CEO: “I have never seen patents sold this way … Generally, companies reach out to buy particular patents from companies. So the buyer makes the first move. I have never seen big companies proactively send email trying to sell patents. Very odd.”
The patent attorney agreed that posting patents is an option. But, many companies use a broker or consultant to research the field, identify companies that might be interested, and assemble a proposal outlining the opportunity and then approach the prospects. If there is enough interest, there could even be an auction. It’s possible that IBM just brought that function in house.
Some wondered if the email was actually an attempt to suss out whether the recipients were infringing on the listed patents. That does not appear to be the case here.
The IBM IP licensing executive who sent the email referred questions to a corporate spokesman. The spokesman said it’s normal for IBM to sell off non-core patents. IBM, which has secured the most U.S. patents for the last 22 years running, reviews its IP portfolio occasionally. Then it opts to divest patents that “do not fully align with the company’s strategic direction,” he said via e-mail.
“Our outreach to potentially interested parties is carefully targeted based on the technology in question,” he added.
He did not speak to the question of whether the e-mailed pitches are new for IBM.
It is worth noting that while IBM is selling off non-core patents on the one hand, on the other it’s busy patenting an array of cloud-related technologies, including some rather basic processes, according to InformationWeek.
Note: This story was updated August 17 with reference to IBM’s cloud patenting activities.
Subscribe to Data Sheet, Fortune’s daily newsletter on the business of technology.