This is an absolutely lovely idea, brought a smile to my face and will hopefully bring a smile to strangers who receive nice messages.
Just as a report, I use enlarged font on my screen so when I installed, the intro developer mail scaled too and without any way to resize the mail windows, the message got cut off, so would be cool if the window was scalable or similar. But, it looks great, is non-obtrusive, low-usage and is a brill idea.