Vectorize or PNG?

Hi if it has any background then use Jpeg file format also try to increase resolution...regards

Fid out the pixel size it displays at. Open it in your browser and take a screenshot. Crop it accurately and see how many pixels. Then prepare your original to that size exactly.

Now, I don't know what gmail does, but if it's a responsive website (sizing according to browser width), it will be scaled regardless and will never be entirely sharp. You don't get sharp images on responsive sites, that's just the reality and you have to live with it.

Another complication is 4K screens. In that case the browser will scale up the image to twice linear dimensions (one image pixel = four screen pixels). This is the standard industry workaround so that the same material can be used whatever screen technology the user has. This 2x scaling, although clean pixel doubling, can be enough to give a slightly blurred impression.