Problem Definition

When the email contains an external attachment, JSM creates the issue with:

!www.site.com/attachment.jpg!

The image is loaded whenever the issue is accessed.

Customers may need to view the issue without the risk of requesting external resources (and getting their access tracked).

Suggested Solution

When Jira Service Management receives an email containing an externally-referencing image, it could download the image, upload it to Atlassian's media servers and present it as an Atlassian-hosted file, rather than presenting the image directly from the external URL.

Or, have an opt-in setting for customers to disable the loading of external resources all together.

Workaround 

Use automation for Jira to update the tags on external attachments: