When inserting a picture, Outlook will rescale the image as if it was a 96dpi image. This issue usually happens when you are using a picture other than 96dpi. This guide contains several solutions and workarounds to this issues. The cause of this issue lies in the way handles image dimensions in combination with its dpi value.
When inserting an image into the message body or using it in your signature, the image can unexpectedly change in size and/or become unsharp when sending even when it still looked sharp when composing.
