The best way to get a chart from Excel into a message (so that it looks the same as shown in Excel), is to do a Ctrl-C (to copy the chart from inside Excel, then open whatever paint program (Paintshop Pro or Photoshop) you prefer to use, then, once open, simple Paste (Ctrl-V) the chart. Both Paintshop Pro and Photoshop will ask you to input the dimensions you want, and in most cases will default to the size you saw inside Excel. Once the image in in place, from the File menu, select "Save As" and choose an image format that's compatible to those allowed in the forum, (GIF, JPG and PNG)
Once you have the saved image, you can import it into a message just as you would any other.
NOTE in saving as JPG: Save with "Chroma Subsampling"s set to "YCbCr 1x1 1x1 1x1 (None)" to reduce the amount of noise. (this is usually found by clicking Options in the save as window that appears)