Notification emails sometimes contain broken images when the images are attached to the blog/page

Issue Summary

When a Confluence user receives a notification email about a blog post/page, the images attached and contained in the notification email sometimes display as broken icons.

Steps to Reproduce

1. Integrate Confluence with a Mail Server
2. Create a test user and ensure that you are watching a space. Additionally, edit the user profile settings to ensure that your mail subscriptions/email settings will ensure that you will be notified for updates.
3. Log in as an admin or another test user and create a blog post OR page with no restrictions in the space that your other test user watches so that they will receive an email notification.

Expected Results

You will be able to see the content and images of the notification email

Actual Results

You are able to see the content (text) of the notification email but the images are broken

Workaround

Do not attach the image to the blog post and instead embed the image as an absolute URL to the image asset.

Additional Testing Notes

• This issue is always reproducible with Gmail web client and Office Outlook desktop client, even while Anonyous Access is enabled.
• Having a valid session with Confluence open at the same time does not have an effect on whether Gmail is able to render the image.
• Issue is not reproducible with Apple iMail desktop client