GREENVILLE, S.C. - A yellowish powder found in an envelope sent to a Greenville County mail service is being tested by the Department of Health and Environmental Control, authorities said.

The envelope was sent to the State Law Enforcement Division after a SourceLink employee noticed the powder on Monday and called authorities, said sheriff's spokesman Sgt. James McCann. A SLED spokeswoman said Wednesday that the health department is testing the substance.

The envelope did not have a return address on it, McCann said.

SourceLink is the largest bulk mailer in South Carolina, company President Dan Jackson said.

The incident comes three weeks after officials removed a package containing the deadly poison ricin from a Greenville postal facility. No one was harmed. Authorities are investigating the incident.

Last weekend, a Clemson University post office employee alerted police after finding a white powder on the outside of a letter. The substance was later determined to be baby powder.