The following are known email display issues with Outlook, especially with Outlook 2016 and 2019 running on Windows.
Contacts viewing your emails in another version of Outlook or in a different email program aren't affected.
Related article: Troubleshooting email display issues
These issues are not unique to emails sent from Envoke, the glitches are with Outlook itself.
Thin lines are inserted in emails in Outlook 2016 (or 2019) on Windows. This is a known bug with Outlook 2016's old Microsoft Word based rendering engine.
Also in Outlook 2016 running on Windows, not all line heights are working as intended. For example line heights of 1.3 and 1.8 look the same.
Background images aren't shown. Read more.
Certain fonts won't show up as specified. A fallback font is used. Read more.
Animated GIFs will only show the first frame of the animation. Check out this great blog post by Litmus for details.
Displaying transparent PNGs doesn't work reliably.
Multi-column layouts don't display well in the Outlook App: the columns don't stack correctly in mobile view. If Outlook App display is critical to you then you should switch to a single column layout that isn't dependent on multiple columns stacking on small screens.