Subscribers sometimes have difficulty in re-sizing their photos to send to the list, so I have created a page showing how to do this in Photoshop. The principles will apply to most other image editing software too.
First, make a copy of the image and work on the copy so that the original is safe.
You need to alter the image size *and* the resolution, so I processed an image to illustrate the method. You will see the document size shown along the bottom of the original image shown below and indicated by the green arrow (it's huge!).
From the Image menu, choose Resize > Image Size, which will bring up a window similar to the following image.
Make sure Scale Styles, Constrain Proportions and Resample Image are all ticked and Bicubic is selected.
Next, you can see I have changed the Width to 400 pixels, which is perfectly adequate for your purpose, and changed the resolution to 72 pixels/inch - most screens display 72 pixels/inch, so there is no point in selecting a larger resolution.
The resized image is now 497K, as you can see below.
You can try variations of this theme to find something which suits your purpose.