As a pixel is 0.75 of a point (at 96DPI), our pixel values can end up uneven (e.g 18px X 0.75 = 13.5pt). Why is this an issue? While Microsoft knows about the bug (and so far have been silent on it), testing suggests the bug appears when Outlook converts pixels to points and ends up with a decimal number.

In applications, 1pt is equal to exactly 1/72th of an inch in traditional print technically 72pt is 0.996264 inches, although I think you'll be forgiven for rounding it up! The 'point' (pt) on the other hand is a fixed unit of length, commonly used to measure the height of a font, but technically capable of measuring any length. So, if a font is 12 pixels in height, that means it takes up 12 pixels on your screen from the top of the letter, to the bottom, which also includes the characters that have sections which are under the guide-line, such as a “p” character. It is a measurement of how tall a font is in pixels which are visible on your computer screen.

This meant that HTML and Cascading Style Sheets (CSS) items not handled by Word were no longer supported (and explains why pre-2007 versions of Outlook are much better at rendering HTML emails).Īs an editor primarily for print media, Microsoft Word (and thus Outlook) uses points (pt) for font size instead of pixels (px). In what many might describe as a backwards step, Outlook 2007 was the first Outlook to switch from Internet Explorer rendering engine to Microsoft Word 2007's. So if it’s not a problem in your HTML, why do these lines appear? On many occasions, we’ve tested the same HTML and seen the bug on one test but not another. What makes this bug so difficult to fix is it’s inconsistency and difficulty to replicate. (the same email test/html with bug appearing in different places in Outlook 2019 120 DPI)

White bar bottomin windows mail