If a project is configured to read a mailbox and publish it's contents, the e-mail reply addresses are used to name you as author of email messages you send to Traction. If you might send email from one of several different email accounts, it's important to list them all.
Your preferred email address (which you select with the radio button) will be the default From address on articles and email replies you send from Traction.
Email digests and email notifications configured by you or by server administrators will, by default, be sent to your preferred email address (unless you choose not to receive digest or email notifications). You can choose to direct digest and notifications to one of your alternative addresses.