For these reasons, the companies offering DNA services for envelopes are drawing a line: These tests are not for living people. The only reason, after all, to resort to getting a living person’s DNA from a letter is if the person is not cooperating with a cheek swab or vial of spit—in which case they probably are not consenting.

This means saying no to potential customers. Joscelyn McBain, the founder of Totheletter DNA, told me that several people have contacted her about testing anonymous poison-pen letters. She’s sympathetic, but she says, “It just opens up a big can of worms.” To avoid testing living people, Totheletter asks customers to explicitly state that the envelope comes from a dead relative. McBain is not against using DNA and genealogy to find violent criminals like the alleged Golden State Killer—she’s actually interested in working with police in Australia—but she’s uncomfortable with using it to track down just anyone.

Read: Should you take a DNA test?

To limit the possibility for abuse in this, MyHeritage does not plan to test items such as toothbrushes, dentures, and old clothing. Since envelopes are usually postmarked and have a sender’s name written on them, it’s easier to validate that the item is what the customer says it is and not some secretly obtained sample. MyHeritage told me it plans to update its terms and services to prohibit uploading DNA profiles of living people that have been obtained through stamps or envelopes. But DNA from dead people, including dead celebrities like Einstein and Churchill, will be allowed.

The ethics of testing a deceased person’s DNA are more ambiguous, says Bettinger. Dead people usually don’t have privacy rights. Dead celebrities, having been public figures, have even less of an expectation of privacy. But dead people still often have living descendants, who share some portion of their ancestors’ DNA and who do have privacy rights. What if Einstein’s living descendants aren’t thrilled about a company uploading his DNA, just so random people online can find out if they’re distantly related to a genius?

On the other hand, says Bettinger, we don’t ask all our living relatives and future unborn descendants for consent when we ourselves mail in a DNA test—even though it affects them all. The alleged Golden State Killer, for example, was identified through third and fourth cousins who took DNA tests. Right now, any one individual has relatively little control over his or her own genetic privacy.

Living DNA’s terms of service would allow testing envelopes for the DNA only when the target person is deceased and the customer has obtained the envelope legally. Of course, these terms of service rely on the honesty of the customer. A lab technician reviews materials to make sure they are what customers claim they are, but cost might be the most practical deterrence. Living DNA’s co-founder, David Nicholson, brought up the example of paternity tests. They’re available in drugstores for around a hundred dollars, while Living DNA’s service costs $400 to $600. “It’s a very expensive way to do that,” says Nicholson.