Labour activist Derek Draper has quit as editor of the LabourList website following the scandal over the proposed No 10 smear campaign.
Mr Draper was sent the notorious email by then Downing Street aide Damian McBride outlining plans to spread scurrilous gossip about senior Tories on a new website to be called Red Rag.
He initially praised the proposals as "absolutely totally brilliant".
In a resignation statement released to The Guardian, Mr Draper acknowledged that his continued presence at LabourList - which was originally set up to discuss serious policy ideas - was detracting from the website.
"I regret ever receiving the infamous email and I regret my stupid, hasty reply. I should have said straight away that the idea was wrong," he said.
"I do ask people to remember that its contents were never published by me or anyone else involved in the Labour party and they would never have seen the light of day were it not for someone hacking into my emails and placing them into the public domain.
"Because of that, a silly idea ultimately destined for the trash can became a national scandal."
Mr Draper is the second casualty of the affair. Mr McBride has already resigned after details of the email were made public over the Easter weekend.