Symptom


Image/logo show as grey box when composing an email.

Recipients preview images OK.



Cause


This bug was introduced in Outlook update: 16.0.6568.2025.


Resolution


Microsoft released a new update build 16.0.6769.2015 that includes the following bug fix:


Fix an issue where images in HTML signatures appear as gray boxes when sending new messages or replying.


You can learn more on the update here: Announcing March feature updates for Office 2016 for Office 365.