You often need to compress PowerPoint presentations when sharing it via email. If your presentation is full of images, you can try compressing these images to reduce the overall size of the presentation.
Once the picture is inserted in the Presentation then click the Compress Pictures option under Format > Picture Tools.
Now be sure to check the Delete cropped areas of pictures option to reduce the overall size of the presentation. Also select the appropriate target output.
Click OK to complete the configuration.