[Cpt.Crashtastic]

In the same Main.php file we can extend the init() function to add a skin for mail

First define the new folder name as a constant

const <MAIL_SKIN_DIR = 'myMailSkin';

then add this line below the line that initializes the main skin dir.

\XLite\Core\Layout::getInstance()->addSkin(static::CUSTOMER_SKIN_DIR, \XLite::CUSTOMER_INTERFACE);

//New Line

\XLite\Core\Layout::getInstance()->addSkin(static::MAIL_SKIN_DIR, \XLite::MAIL_INTERFACE);

There are other skins you can alter!