Mr McBride resigned on Saturday over the e-mails
Former Downing Street adviser Damian McBride's actions were a "clear and serious breach" of Whitehall rules, the head of the civil service has said.
Sir Gus O'Donnell said advisers who spread "inappropriate material" would be automatically sacked under a new code of conduct rules.
Mr McBride quit after making unfounded e-mail slurs about senior Tories.
Meanwhile Derek Draper, who received and responded to the e-mails, will no longer advise Labour, the party says.
In a letter, Sir Gus said Mr McBride's behaviour "cannot and has not been tolerated" and fell "far short" of people's expectations.
He wrote to shadow Cabinet Office minister Francis Maude after he asked a series of questions about who knew what about e-mails from Mr McBride to Mr Draper - a former aide to Lord Mandelson.
These contained allegations about Tory leader David Cameron and shadow chancellor George Osborne and others which, it was suggested, could be published on a Labour-backing gossip-led website called Red Rag.
Mr Maude questioned the role of Cabinet Office minister Tom Watson - who has issued a statement through lawyers saying he had "no involvement in or knowledge of" proposals to set up Red Rag.
He also asked whether the e-mails were part of a "broader pattern of activity by other special advisers".
In his reply, Sir Gus said Mr McBride was "no longer employed as a special adviser" and had "not received severance pay".
He said Mr Watson had "made his own position clear" and the prime minister had made clear "that he has been assured that no minister or political adviser other than Damian McBride had any knowledge of, or involvement in, the e-mails".
Sir Gus also said he had written to the heads of all Whitehall departments with "strengthened" guidance on codes of conduct. Special advisers will be required to sign an undertaking that they are aware of the new guidance.
For the Conservatives, shadow schools minister Nick Gibb said the old code had already banned personal attacks and the entire affair demonstrated "something very specific to Gordon Brown".
"It isn't about strengthening the code that matters; it's about changing the culture around Downing Street and around Gordon Brown," he said.
Liberal Democrat leader Nick Clegg said the episode showed an "appalling lack of judgment on Gordon Brown's behalf".
Mr Draper has said he "deeply" regrets responding to Mr McBride's e-mail and was considering resigning from his role running LabourList, a Labour-supporting website.
On Wednesday, in an e-mail to members of Labour's National Executive Committee, the party's general secretary, Ray Collins, said Mr Draper - who had offered "advice and opinion on an ad hoc basis" - would not be asked for either again.
"I decide what advice I take or seek and act in a manner appropriate with my values and those of the party which certainly does not include smears or personal attacks," he said in the email, which was published on Conservative blogger Iain Dale's website.
Mr Brown has written to those named in the e-mails to express his "deep regret" and had sent a letter to Sir Gus, saying he was ready to take "whatever action is required" to prevent a repeat of the incident.
Meanwhile, the Times newspaper has reported that the Red Rag website was set up by someone giving the name "Ollie Cromwell" and the House of Commons as their address.
Internet registration organisation Nominet confirmed that was the address given and is looking into whether its terms and conditions were breached.
The government has received a series of freedom of information requests demanding more information about Mr McBride's e-mails.