JIRA Service Desk - Email Channel - Ability for customers to add comments via email without creating issues

Is there a way for customers to add comments via email on their service desk portal tickets? Without giving them the permission to create new issues via email?

Our customer tickets have certain fields we want to keep required, which prevents us from using the email channel; however we want to give customers the ability to add comments to JIRA service desk notification emails via email. Is this possible?