PORTLAND — A Sanford man charged with emailing sexually explicit videos of children to an undercover federal agent has pleaded guilty.

Richard Moulton Jr. entered his plea Wednesday in U.S. District Court in Portland to a charge of transportation of child pornography.

Authorities say the 30-year-old Moulton was arrested following a Feb. 28 email exchange in which he sent an agent of Homeland Security Investigations four videos. Prosecutors say each video depicted a child or children between the ages of 4 and 12 engaged in sex acts.

They were sent in response to the agent’s sending of a picture of what appeared to be a young girl.

Moulton is scheduled to be sentenced Sept. 9. He faces a maximum of 20 years in prison.