After using Jira Service Desk for a while we ran into a problem with automatic re-opening tickets when a customer replied to a closed ticket. The automatic re-open worked fine but any attachments where just thrown away. Usually customers respond back with a screenshots, logs or similar information needed to further investigate the ticket.
At the end of the comment that triggered the re-open and contained an attachment the following error message was added: Failed to add the following attachment to this issue because file attachments are disabled for the system.
Did a lot of research online without finding any solution, a lot of people had the problem but no suggested solutions. After some testing I realized that when the e-mail gets ingested by Jira Service Desk the contents of the e-mail is added as a comment and any attachments to the e-mail is attached to the case. After this occurs the ticket is automatically re-opened due to the customer comment. A closed or resolved ticket can not get new attachments and since Jira Service Desk is trying to attach the file before the ticket is re-opened it fails.
The simple solution to this is to add a property on the Closed workflow step for the Jira Service Desk project. If you edit your workflow and click the Closed step then open up the Properties, here you can add a new property key jira.issue.editable with the value true. This will allow closed issues to be edited which will make sure that the attachments are added during the re-open process. The only drawback with this is the Edit button being visible on closed cases.