Some email providers, including Yahoo! and AOL, prohibit any third party (such as Submittable) from sending email on behalf of their customers. This is a security measure to prevent spam and forgery. To prevent these messages from bouncing, Submittable overrides sender email addresses for AOL and Yahoo! email accounts so that they come from the email address firstname.lastname@example.org.
If you would like your emails to show a different sender email address, you may use an organization or personal account email address that is not from a Yahoo! or AOL account.
For more information, please visit https://help.yahoo.com/kb/SLN24016.html and http://postmaster-blog.aol.com/2014/04/22/aol-mail-updates-dmarc-policy-to-reject/.