Prepare email images for the width of their content block and the clients your recipients use. A smaller image can reduce downloading, but it does not guarantee inbox placement, instant rendering or a particular engagement rate. Keep essential information in readable email text so the message still works when images are blocked.
Measure the template before resizing
An email builder can have several template widths and column arrangements. Mailchimp, for example, distinguishes its new and legacy builders and gives different image width ranges for them. Use the current recommendation for your actual block, not a universal 600-pixel rule.
Illustrative example: a 300 CSS-pixel product image might use a 600-pixel source for a denser display. Inspect the real message to decide whether that detail is useful; increasing source dimensions also increases potential bytes.
Choose formats for the recipients
JPEG is a useful starting point for photographs and PNG for suitable graphics or transparency. Check client support before relying on newer formats. For animation, make the first frame meaningful and test whether the intended clients play the full sequence. A still-image compressor is not an animation converter.
Compare exports, not arbitrary maximums
Make candidates from the original and compare fine text, product detail and edge quality at the message display size. Set a practical budget for the whole email image set, then allocate it by role. Quality numbers and byte targets are starting points you evaluate, not universal deliverability standards.
Send and inspect the actual email
Select files locally in ZipMyImages; image processing does not upload them to a conversion server. Upload the chosen exports to your email service afterward. Send a test to representative desktop and mobile clients, check blocked-image behavior and confirm links and alternative text. The email service may resize assets, so inspect its delivered version rather than only the file on your computer.