This page provides details of known email display issues with some versions of Outlook, notably Outlook 2016 and 2019. These issues are not unique to emails sent from Envoke, the glitches are with Outlook itself.
Most email recipients don't use Outlook
Contacts viewing your emails in another version of Outlook or in a different email client (Gmail, Apple, etc) aren't affected.
Overall, less than 6% of email recipients use Outlook and not all of them use versions that are prone to display issues. You can view the latest global email client market share breakdown here and you can view opens by email client for your email campaigns on the main email reports page from your account.
Known display issues in Outlook
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. Read more at the bottom of this page under the Additional details related to thin white lines in emails in Outlook headline.
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.
When headlines wrap in Outlook, often a larger line height gap will appear than in other email programs.
In other cases, Outlook may add 20 - 30% more line height than expected.
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.
Select versions of Outlook (360, 2019 and 2021) might show a band of background colour around partial width, left or right aligned images when using image blocks. An example of this is a small logo aligned right in the message header. The recommended workaround is to create a header image that is the full width of the header block (660px), and centre aligned, to display the header without this artifact.
Many emails that are sent to newer versions of Outlook are shown with fully justified text with words auto-hyphenated when the email is not sent that way from the sender. These settings, called Use Smart Justification and Use Hyphenation can be turned off in Outlook as per their support article.
Some versions of outlook.com add additional spacing above and below headlines.
Additional details related to thin white lines in emails in Outlook
This is a well documented issue in the email developer community. The line shows in seemingly random areas. Despite Microsoft being aware of this bug there is no plan to fix it.
The leading theory among the development community for the cause is that it comes from the pixel to point conversion that Outlook does, when a line-height, height or font-size is converted from px to pt and ends up as a decimal, the leftover decimal point is added as an ugly white line.
A suggestion is to adjust line-heights and font sizes to be even numbers, preferably divisible by four. This is not a guaranteed fix but it's been recommended by some developers.
The new version of Outlook that’s scheduled for 2026 may put an end to this and other Outlook bugs.