Email has been the source of constant headaches for Hillary Clinton, but this time the email news has nothing to do with a private server in Chappaqua, N.Y.: It appears that the Clinton campaign recently received an influx of potentially lucrative email addresses, possibly a transfer from the Democratic National Committee.
Email measurement firm Return Path says the Clinton campaign's email database has nearly doubled in size since mid-June, linking the campaign to a larger pool of potential donors.
According to the company, which evaluates email campaigns using estimates based on its panel of 2.5 million active email users, the number of addresses that the Clinton campaign sent messages to grew 93% as of June 14, compared to the previous week, and has remained the same size since then. The growth represents only emails sent directly from the Clinton campaign, according to Return Path.
The research comes on the heels of the FBI's decision not to recommend criminal charges against Ms. Clinton for using a private email server while discussing sometimes-classified information as secretary of state.
According to Return Path, the Clinton campaign list is more than 1000% larger than that of presumptive Republican presidential nominee Donald Trump. The actual number of email subscribers in the Clinton camp's list is not publicly available, though it is likely to be in the multi-millions.
The Democratic National Committee and the Clinton campaign did not respond to requests to comment for this story.
"She has probably been one of the larger lists," said Tom Sather, senior director of research at Return Path, who said duplicate emails or profiles were most likely removed during the integration process.
When there is such a large increase in the size of an email list, the growth is probably not the result of people volunteering their addresses to a campaign. Rather, it is likely the result of a list purchase or transfer.
Purchasing email lists or paying to send email messages to subscribers of publications such as partisan news sites is a common and legal practice in political campaigning. CAN-SPAM law governing commercial email does not apply to political campaigns.
During the 2014 midterm elections, voter data, analytics and predictive models from President Obama's 2008 and 2012 campaigns were made available to Democratic candidates via the DNC's database. However, it wasn't until around a year ago that Obama supporter email addresses were handed over to the DNC.
The fortification of the Clinton campaign email list does not necessarily indicate a direct infusion of Obama supporter email data into the Clinton campaign's email system.
But closer coordination between the Democratic Party and the Clinton camp is to be expected as the presidential campaign shifts from primary to general election mode.
An increase in list size is one thing, but whether those emails are deliverable and accepted by recipients is another. So far, Return Path research shows that Clinton campaign emails sent since June 14 have not resulted in an uptick in spam complaints among recipients. "We're not seeing a significant change in her engagement in a negative way," said Mr. Sather. The Clinton campaign's spam rate has been at or around zero percent throughout the election season.
"You would think that they would see a decline in email deliveries for her if she's emailing a bunch of new people," said Democratic digital consultant Colin Delany of Epolitics.com. He added that while some Bernie Sanders supporters might not appreciate receiving emails from the Clinton campaign, "The ones who are still angry enough at Clinton to mark her email as spam are probably the less likely ones to be on the DNC list in the first place."