Why are emails into tickets being treated as internal comments?

[Francesco C]

We have noticed that when our end users are attempting to send in an attachment (usually for validation of a change that has been completed) via email to a ticket, JIRA thinks they are trying to create an internal comment and blocks the e-mail if they are not a participant on the request (or an agent).

How do we force JIRA to treat net new emails into a ticket (with ticket in subject line) as public comments? This is not a reply to any notification but an email generated by an end user to comment on a request.

[Jack Brickey]

Are you talking Jira Software here or Jira Service Desk? I ask as this is posted in Jira not JSD but you mention agents. 

if the user sending in an email is a customer of the project it should be a public comment. If they are an internal JSW user collaborating on JSD issue, I.e. not agents it will be internal. 

[Francesco C]

This is JSD and the user is a customer of the project. When they went to e-mail in, their comment never posted. Checking the mail log, it says the user doesnt have permission to post internal comments.