WASHINGTON—Newly released emails from Hillary Clinton show that former Clinton White House aide Sidney Blumenthal remained a political confidant and correspondent throughout her time as secretary of state.

The largest batch of Mrs. Clinton’s emails to date—some 7,000 pages—was released by the State Department Monday night, offering a glimpse into her small circle of advisers and gatekeepers at the State Department.

The department has now deemed about 125 emails in the latest release classified. The classified material appears in redacted form, occasionally in emails discussing internal operations and personnel.

State Department spokesman Mark Toner said that all the emails weren’t classified when sent but have since been retroactively made classified.

Mrs. Clinton corresponded mostly with a tight-knit circle of State Department aides, along with Mr. Blumenthal who filled her inbox with policy missives, domestic political gossip and information about foreign governments.