We are using Dynamics 365 on-premises.
There is an issue with images in email HTML body:
If user create an email from CRM and insert an image in email body, then send this email, the images are displayed everywhere (in CRM and another app, Outlook for example). In this case, the image in the email is encoded in base64.

However, if we receive an email from another source in CRM or reply to an email received from CRM, the email contains the image as an attachment.
In one editor (by default Text Area control for Email entity), the image is displayed (with a source link on blob).
In another RTE editor control, the image is not displayed, and its source link is 'cid:' schema.
If user reply to an email with such an image from any editor, the image is not converted to base64, and the recipient does not see it. This behavior may be due to the image remaining in CRM.
What should be done about this behavior?
So, we have two issues:
1)Why do we not see the image in the RTE control, which actually exists in the attachment but its source is 'cid:'? (Although in another control, by default, we see the image and its source is /blob/)
2)What should be done with emails from replies where the image was already in the email body and was added to the attachment? When forwarding/replying to such an email, the image is not sent to the recipient.