And 21.3 percent of campaign emails wound up in spam, which poses a problem for presidential candidates looking to engage with potential voters and donors. By comparison, Len Shneyder, Twilio’s vice president of industry relations and author of the report, said in an interview that 16 percent and 18 percent of all emails from private companies don’t reach consumers’ inboxes — either they go to spam or are bounced back to the sender. Twilio’s study of campaign emails was only able to measure those that landed in the spam folder.

Shneyder said the campaign emails could be landing in Gmail’s spam folder for a variety of reasons, including suspicious text in the body of the email or having email lists that include suspicious recipient addresses.

“Now, the caveat to that is if you interact a lot with a brand” or are “constantly opening” and “clicking the links” in an email, he said, then Google views it as “highly relevant to you” and could start sending it to your primary tab.

During the observation period, Twilio’s Gmail account received a total of 811 emails from the campaigns, with each sending an average of 1.5 emails per day. Half sent an email on a daily basis, the study shows.

And, as is common practice, the campaigns tended to tie their emails to the news cycle: On July 31, the second day of CNN’s Democratic debate, Twilio’s test account received its largest set of messages at 60 total — averaging at about three per campaign that day urging people to donate and watch the debates.