Images are generally included in an email by either linking or embedding. The filesize for the images is important because the receivers will need to download them. Either on opening (linked images) or fetching the email (embedded images). An email with larger imagefiles included will load slower which leads to less conversion.

Image dimensions, resolution and compression can be changed to reduce image filesize:

  • dimensions: a mailing is usually created with 600-700px width. Images can be created on 2x size for a sharper display so an image should have max width of 1200-1400px with a relative height
  • resolution: an image for screen purpose does not need a 300dpi resolution. 72-96dpi will usually do just fine
  • compression: jpeg or png image files can be compressed with image editing software. Usually compressing upto 70% is without visible quality loss

Generally, an image larger than 1mb is considered large and a mailing totalling more than 5mb is usually considered large.