The letter to Donald Trump Jr. that contained a suspicious white powder and landed his wife in the hospital said, “You are getting what you deserve,’’ according to law-enforcement sources.

“You are an awful person. This is why people hate you. You are getting what you deserve. So shut the f–k up,” sneered the letter-writer, sources said Tuesday.

The note, in an envelope postmarked in Boston, was delivered to the Upper East Side home of Donald Jr.’s mother-in-law at around 10 a.m. Monday, officials said.

Donald Jr.’s wife, Vanessa, opened the envelope and discovered the powdery substance and note, sources said.

Realizing the potential danger of the powder, a panicked Vanessa then ran out of the room, stashed the letter and powder in a plastic bag and called 911.

She was rushed to the hospital as a precaution.

The substance is believed to be cornstarch, sources have said.

The letter was not sent directly to the couple’s own Manhattan address, because it was more likely to get through security, according to the sources.

“This is not a secure site,’’ a source had said of the Sutton Place home of Vanessa’s mom, Bonnie Haydon.

“Secret Service is not going through [the] mail.’’

Vanessa, a former model, and her husband, the eldest child of President Trump, surfaced Tuesday morning for the first time since the frightening incident, leaving their building with two of their five kids in tow, surrounded by Secret Service agents.

Vanessa returned to the building hours later with at least one of the children.

None of the kids was present when she opened the envelope, sources have said.

The new details about the letter’s contents came amid reports that Washington, DC, cops are investigating a mysterious “white substance” sent to former President Barack Obama’s office.

Fox 5 TV said the delivery of the letter to Obama was reported to authorities at around 12:30 p.m.

Obama has leased space at the 24th Street Northwest building, owned by the nonprofit World Wildlife Fund, which has its headquarters there, since leaving office in January 2017.

Traffic was heavy in the vicinity as emergency responders arrived to investigate the incident.

Additional reporting by Bob Fredericks and Kevin Fasick