Font size may differ from the size in the original email from Outlook for Mac
Original KB number: 2783553
This article describes a by design behavior that email messages that are sent from Microsoft Outlook 2016 for Mac or Outlook for Mac 2011 to other operating systems may have with a different font size than the original email message font size.
For example, when text that has Calibri font size 14 is sent from Outlook for Mac to Microsoft Outlook for Windows or Outlook Web App, the text may be displayed as a font size other than 14 when the message is received on the other operating system.
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This is caused by the pixel-to-point or point-to-pixel conversion that happens between the Mac and Windows operating systems.