There is not an option for this. Users need to have an account to open issues. They can be automatically added as @Alex Christensen indicates. If they only ever use email for opening/commenting on issues then not login required but if they use the portal then they need to login.
Hello Atlassian Community! I'm Teresa, the Product Marketing Manager for Jira Service Desk Server at Atlassian. I'm excited to announce two exciting releases for Jira Service De...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs