If the "mail checker" icon on the panel is used, it would be nice if the icon for no mail/mail was configurable by the user. (ie. two icons would be specified - once for standard, and the other for new mail...) Reproducible: Always Steps to Reproduce: 1. 2. 3.
The icon follows the icon theme, so you should be able to change the icon by adding a custom xfce-mail.png or xfce-mail.svg icon to your current icon theme. Try e.g. creating a ~/.icons/hicolor/48x48/apps/xfce-mail.png. I think I'm not going to change this behaviour.
Alright, I'm not going to change this for 4.2. For 4.4 I think I'll remove the mail checker from the main panel and I hope there can be a better solution, either with an external plugin or with a systray icon. Thanks for the report.