Did EPA Chief Lisa Jackson resign because emails she sent from a secret alias account will go public next month?

Daily Mail
"It was revealed in November that EPA Chief Lisa Jackson, 50, had sent thousands of emails tied to coal regulation from a secret alias account - The EPA chief announced on Thursday that she will resign after four years on the job for ‘new challenges, time with my family and new opportunities to make a difference’ - Chris Horner, of the Competitive Enterprise Institute, said the scrutiny over the alias emails regarding the Obama administration's alleged ‘war on coal,’ is clearly a factor behind Jackson’s decision to step down - Jackson's resignation is effective following the President's State of the Union address next month"