:-) (with apologies to Ian)
It’s all in the extended headers of the mail message. You can view these headers using suitable menu options in your mail reader.
> Like this:
>
>> X-Mailer: QUALCOMM Windows Eudora Version 7.1.0.9
>
> Eudora? That's so 20th century.
Not to mention the idea of mobile chip manufacturer buying an email software vendor. Seriously, what was that all about?!(*)
—ravi
(*) rhetorical question