If your client can't see digest, it is most likely one of the two reasons:
A browser issue: Ask your client to switch to Chrome. If they are using Chrome, ask them to try opening it in incognito or have them clear their cache & cookies.
They're using a VPN: The client may be opening email through their VPN (like Citrix). Ask your client to open the email from their desktop directly.
Troubleshooting browser issue -
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