Issue Summary

When customer sends email with embedded images in the signature part.
JSM mail handler signature detection will hide it under the "Signature", but embedded images inside of the signature will have "Preview unavailable" error.

Steps to Reproduce

1. Go to: jira/settings/products/jira-service-management-email-requests (Product > Email Requests) 
2. Add custom "Use custom text to detect and hide signatures" with text "Thanks in advance"
3. Create an email with text and add embedded Image
4. Under it add "Thanks in advance" text and add an imbedded image as signature
5. Send email to the JSM mail handler

Sample email body:

Expected Results

The embedded images in "Signature" have preview.

Actual Results

The embedded images in "Signature" have "Preview unavailable" error.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available