Use a signature file. That way your image resizing will be stored. See https://support.mozilla.org/en-US/kb/signatures#w_signatures-stored-in-files What is the file type of this image signature. I would hope PNG or JPG as other formats are either large file to make your email large or are not commonly supported. Note also that having an image as the last thing in the email may see it flagged as spam in some mail servers receiving your mail. Image spam typically has no text after the image. So it might be a good idea to include some text after the image, like your name, job title or phone number.