If you are experiencing an issue when viewing your email on Outlook and noticing the sudden appearance of an unexpected white line across your screen (shown below), read this article for some helpful tips to mitigate this problem.
Why do these lines appear?
These white lines are caused by a glitch with how Outlook scales content on screen.
Office products were originally intended for the creation of printed documents, so they use points (pt) rather than pixels (px) as measurement units.
They convert any pixel values to points on the fly when displaying on-screen content.
Since 1px = 0.75pt, this conversion can result in fractional values that can’t resolve nicely to whole pixels on the screen, so you get these visual artefacts.
Sadly it’s not possible to completely avoid the issue, only to mitigate it.
Some tips for avoiding it are:
Use whole, even numbers for things like spacers and top and bottom padding on elements (ie 20px instead of 21px, and 30px instead of 30.5px)
Add some extra padding or a line break to any particular area that is causing problems
Try to make image widths and heights a whole, even number
It's not always easy when you are using modules, but if you are seeing hairlines in the joins between sections, it helps to consolidate more content inside fewer sections, as shown below. This means there are fewer structural gaps where the lines can show through.
Note: Microsoft is releasing a completely overhauled version of Outlook over the next few years (which uses the Outlook.com rendering under the hood) which will completely remove this issue.
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