Is there a way to link emails with Jira issues, emails that come form external users without a jira account in our instance

[Bernardo San Juan]

Any plugin, or any way to deal for instance, when some JIRA user forwards an email from a JIRA issue to a person who has not got an account in Jira. This person responds to the email but it is not shown on the JIRA issue. 

Any interesting plugin to manage emails within Jira? something that offers more options than the "incoming mail" tab within  JIRA system

[Chris Cooke Old Street Apps]

Have you tried External Share for Jira? It's useful because it offers a live view of Jira issues, and boards without using up licenses, and makes it very easy to email issues to external users, while letting them watch, comment or add attachments.

Let me know if this helps!

[AgentSmith]

In the project permissions for the project(s) in question, you can define the Browse Projects permission with Group(Anyone). Then you can use the share feature to send issues. I've included reference materials below. 

Project Permissions:

https://confluence.atlassian.com/display/Cloud/Managing+Project+Permissions

Sharing Issues: 

https://confluence.atlassian.com/display/Cloud/Emailing+an+Issue