[exim] passive OS fingerprinting

I found this email from 2006:
http://www.mail-archive.com/exim-users@exim.org/msg17775.html
about passive OS fingerprinting.

Does anyone know if there is another way of doing this?

Thanks,
Jeroen

--
http://goldmark.org/jeff/stupid-disclaimers/
http://linuxmafia.com/~rick/faq/plural-of-virus.html