Financial terms of the deal were not disclosed.
The companies said they would merge the two conferences, with Golden Group producing INBOX-the Email Event once a year on the West Coast and once on the East Coast.
"We wanted to build a home for the messaging and e-mail industry," said Martin Hall, VP-strategy for Golden Group and managing director of INBOX.
Richard Snee, managing director of ETC, said the company had other suitors. "There were many larger traditional publishing entities interested in the ETC show and the development of it, but it was very easy for me to make a decision to go with [Golden]," he said. "They have a passion about serving the [messaging] community."