You are working with a small image on something like an e-mail so smaller is better. I found this link https://avada.io/resources/ideal-email-image-size.html#:~:text=The%20best%20email%20image%20size,exp.... 

Adjust according to the ratio that your current image is. I probably did a dozen trials before I got it right when I did it as a letterhead. I don't like LINK, so I have not spent time with what you are doing.