In the email, which has leaked onto the web after his departure earlier this week, Stewart Butterfield compared himself to a ‘tinsmith’ whose skills were no longer relevant in a multinational conglomerate.
Mr Butterfield, who created the site with his wife Caterina Fake, said he had been ‘cast adrift’, adding that it was time for him to make way for a ‘new generation’.
The couple, who have both left the company, sold Flickr in 2005 to the online search and media giant for $35m.
In the message to Yahoo vice president Brad Garlinghouse, Mr Butterfield likened his length of service to 87 years and the company to a tin-smithy that had moved away from its roots.
“I don’t need no fancy parties or gold watches (I still have the one from ’61 and ’76),” he said. “I will be spending more time with my family, tending to my small but growing alpaca herd, and, of course, getting back to working with tin, my first love.”
Yahoo! confirmed the resignations and said Kakul Srivastava was now serving as general manager at Flickr.
“Stewart Butterfield and Caterina Fake have made tremendous contributions to Yahoo over the years,” said a Yahoo spokeswoman. “We greatly appreciate all their work and dedication and wish them well in their new endeavours.”
Despite having seen off a takeover bid from Microsoft earlier this year, Yahoo! faces an unprecedented brain drain of other key players.
In the last few weeks, executive vice president Jeff Weiner has quit, alongside the head of research Usama Fayyad.
The company has also cut more than 1,000 jobs in recent months, as well as announcing plans to move its UK operation to Switzerland to reduce costs.