WordPress.org

What it does, how it works:

It's pretty straightforward, really. Simply set a logo in the options and from that point forward, as long as the plugin is active, the logo that you set will be sent with all emails that are processed by the wp_mail function (this includes new user registration, password reset, comment follow-ups and more). This plugin is probably especially handy for e-commerce sites that want to strenghten their brand.

Please keep in mind, this is free software that has no guarantee that it is suitable for any purpose