Thank you Ray for your suggestions.
I had some success with it, while making me realize where the limits of this old Dynamics version are.
First I had to fix our Exchange. It was for some reason sending mails from 3rd party apps like Dynamics as text encoded only, while Outlook worked properly so we were not aware of this setting.
Had to use this command in Exchange Management shell to see it:
Get-RemoteDomain | fl
It said this for the "*" domain representing any (external) domain, among many other settings:
...
ContentType : MimeText
...
So I had to run this to force it to send both Text and HTML as expected by most email clients to give the user a choice:
Set-RemoteDomain -Identity * -ContentType MimeHtmlText
or to send HTML only:
Set-RemoteDomain -Identity * -ContentType MimeHtml
Before that, all outgoing mails from 3rd party apps were text encoded only.
With the help of your suggestion I was then able to create a few test mails copying the signature first (from Outlook) and then additionally copying the images having the src set to a base64 encoded data chunk of the PNG image.
I sent the same email from outlook.
Outlook is then taking the img and converts it into an attachment, which Yahoo then displays correctly.
If I send it through Dynamics, this conversion does not happen and unfortunately Yahoo does not display the image at all (even though it is in the technically correct HTML). Here is a brief description of how it should be done (just like Outlook already does it):
https://stackoverflow.com/questions/9110091/base64-encoded-images-in-email-signatures. If changing the image source to a hosted image this would probably work, which I have seen in other community postings. But this would get intercepted by many security solutions because it is like a tracking cookie and it is possible for the sender to see (if not blocked) who opened the email (if using a unique image URL) and from where it was opened and eventually more information like browser used and so on.
Another bad thing I noticed was that there is no ability to copy & paste into a Dynamics Mail and resize the image. It always stays at its original size. We insert screenshots or images of dialogs a lot during our work. I don't think it makes any sense to further look into 8.2 unless I could get the Outlook CRM Client working and then use Outlook like before.
Instead I have now setup a Dynamics 9.2 Azure installation to check out what it can do. Most likely many of these issues have been addressed already in 9.x.
Thanks again.
Best regards,
Andreas