Version:           KMail/1.9.7 (using KDE 3.5.8)
Installed from:    Fedora RPMs
OS:                Linux

Observed at vger.kernel.org Postmaster inspection logs of "TABOOed because of headers with errors":

 From:   Frans Pop <elendil@planet.nl>
 Illegal-Object: Syntax error in To: address found on vger.kernel.org:
        To:     David S.Miller <davem@davemloft.net>
                        ^      ^-missing end of address
                 \-extraneous tokens in address
 Subject: [2.6.25-rc2] System freezes ~1 minute after logging into KDE
 Date:   Sat, 16 Feb 2008 20:14:00 +0100
 User-Agent: KMail/1.9.7

What the KMail should have produced is:

     To:  "David S. Miller" <davem@davemloft.net>

The dot is so called special in RFC-2822 defined header syntax, and in order to have them outside actual addresses, they must be inside a quote-pair.  Meaning that whole names must be in quotes.

I do not use kde myself, but you are welcome to ask the Email Syntax Oracle about test fixes at address:

   autoanswer@vger.kernel.org

It sends back the headers of the email that you sent to it, including syntax markers.