Email header size
Export at 1200 wide and set width="600" for retina.
Cropped in your browser · your image is never uploaded
600 pixels wide is the safe email width, unchanged for two decades because it fits the narrowest common preview pane. Export at 1200 and set the width attribute to 600 so it stays sharp on high-density screens.
How to use the email header size
The bigger design constraint is not the width but that many clients block images by default, and a header that carries the entire message becomes a blank rectangle. Anything essential belongs in live text, with the image as reinforcement, and every image needs alt text, because that is what the reader sees when it is blocked. Dark mode is the newer problem: several clients invert backgrounds, so a logo saved as black-on-transparent becomes invisible. A white or brand-coloured background on the logo avoids it. Keep the file under about 200 KB; several clients clip messages that get too large.
Questions
600 pixels. It has been the standard for two decades because it fits the narrowest preview panes.
Export at double size; 1200 wide, and set the HTML width attribute to 600.
The reader sees your alt text and nothing else. Never put essential information only in an image.
Yes. Some clients invert backgrounds, so a black-on-transparent logo disappears. Give it a solid background.
About 200 KB. Some clients clip large messages entirely.